How to Control Container Run Order using Docker-Compose?

Docker’s health check and Spring Boot apps

Photo by Brett Jordan via Unsplash

Introduction

In this article, I will describe how the Docker HEALTHCHECK statement can be used to characterize the dependencies between containers inside the docker-compose.ymlfile and how it can be used to set the order in which containers will be run.

What is a health check?

In the context of Docker, health check is used to check if a container is still running. If you are familiar with Kubernetes, you probably thought of Liveness and Readiness probes — and it’s actually a good association!

Often the fact that a container is working does not mean that it is ready to receive traffic. This is well described on the Kubernetes documentation page on probes, but…. what about Docker?

Don’t worry — Docker also has a built-in mechanism for verifying the state of a container, and you can use it either in the Dockerfile images or in the docker-compose.yml file.

Docker Compose and the startup order

Docker Compose has a built-in startup order mechanism, but as it is mentioned in the documentation:

On startup, Compose does not wait until a container is “ready”, only until it’s running.

The example you will meet most often is the simple use of the depends_on instruction in a Compose file, such as some service depends on a database. Below is an example taken from the docs:

services:
  web:
    build: .
    depends_on:
      - db
      - redis
  redis:
    image: redis
  db:
    image: postgres

It works, however, it is only the short syntax of this instruction! In the long syntax you can also specify a condition:

services:
  web:
    build: .
    depends_on:
      db:
        condition: service_healthy
      redis:
        condition: service_started
  redis:
    image: redis
  db:
    image: postgres

Let’s see how it can be useful for Spring Boot applications.

Use case

I’ve been playing around with Spring Cloud Config Server lately and wanted to run it and my sample Config Client microservice using Docker Compose. I had my Config Client microservice configured to fail quickly if Config Server is not running:

spring:
  cloud:
    config:
      fail-fast: true

And even though I had a dependency configured inside my compose file…it failed! It turned out that the Config Server container is running, but the application is not ready yet!

Luckily, I was able to fix it with:

• Spring Boot Actuator and its /actuator/health/readiness probe
• healthcheck instruction in docker-compose.yml file
• depends_on instruction in docker-compose.yml file, but using long syntax

In the following tutorial, I will show you what my initial approach was and how I managed to fix the problem. Let’s go!

Demo

The code will be available in my GitHub repository — I’ll just focus on the most important parts below.

Config Server

Lets get started with Config Server. This project will only require 2 additional Spring Boot dependencies:

• spring-boot-starter-actuator
• spring-cloud-config-server

I added @EnableConfigServer above the application’s main class, and configured application.yml file:

server:
  port: 8888
  shutdown: graceful

spring:
  application:
    name: config-server
  profiles:
    active: native
  cloud:
    config:
      server:
        native:
          search-locations:
            - classpath:/config

management:
  endpoints:
    web:
      exposure:
        include: "health,refresh"
  health:
    readiness-state:
      enabled: true
    liveness-state:
      enabled: true
  endpoint:
    health:
      probes:
        enabled: true

A few properties worth mentioning:

• spring.profiles.active — I used the native profile, and…
• spring.cloud.config.server.native.search-locations — config server will search for configuration files in src/main/resources/config directory;
• management.endpoints.** — I’ve enabled Actuator’s liveness and readiness probes — a very cool feature! I will use one of these probes for Docker’s health check.

Later, I added the simple-microservice.yml file under the src/main/resources/config directory:

server:
  port: 8080

management:
  endpoints:
    web:
      exposure:
        include: "health,refresh"
  health:
    readiness-state:
      enabled: true
    liveness-state:
      enabled: true
  endpoint:
    health:
      probes:
        enabled: true

example:
  key: example-value

That’s it. After that, let’s build the .jar file:

mvn -DskipTests clean package

And create a Dockerfile:

FROM openjdk:17-slim as builder
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} application.jar
RUN java -Djarmode=layertools -jar application.jar extract

FROM eclipse-temurin:17-jre-alpine

ENV JDK_JAVA_OPTIONS="-Xms256m -Xmx512m"

RUN apk --no-cache add bash curl

RUN mkdir /app
RUN addgroup -S spring && adduser -S spring -G spring
WORKDIR /app

COPY --from=builder dependencies/ /app
COPY --from=builder spring-boot-loader/ /app
COPY --from=builder snapshot-dependencies/ /app
COPY --from=builder application/ /app

RUN chown -R spring:spring .
USER spring:spring

ENTRYPOINT ["java", "-Djava.security.egd=file:/dev/./urandom", "-cp", "BOOT-INF/classes:BOOT-INF/lib/*", "pl.akolata.healthcheck.demo.configserver.ConfigServerApplication"]

Then see if it works…

docker build . \
  --tag spring-boot-healthcheck-demo/config-service:latest

docker run \
  --rm \
  --name=spring-boot-healthcheck-demo-config-service \
  -p 8888:8888 \
  spring-boot-healthcheck-demo/config-service:latest

curl -X GET http://localhost:8888/actuator/health/readiness
{"status":"UP"}%

Good! Let me summarize:

• Config Server application is configured and running with native profile
• its configuration enables Actuator’s /readiness probe
• the application itself can run in a container, based on the above Dockerfile

Config Client (named “simple-microservice”)

Dependencies needed:

• spring-boot-starter-actuator
• spring-cloud-starter-config

It will be much simpler that the previous app. Its src/main/resources/application.yml file looks like this:

spring:
  application:
    name: simple-microservice
  config:
    import: "optional:configserver:"
  cloud:
    config:
      fail-fast: true

• spring.application.name — the application will attempt to retrieve the simple-microservice.yml file from the Config Server (and others, depending on the profile, but for more details see the Config Server documentation)
• spring.config.import — the provided value will, by default, attempt to access Config Server at http://localhost:8888
• spring.cloud.config.fail-fast — if the Config Server is not available, the application will fail immediately

At this point you can create .jar file, copy the previous Dockerfile and build the image in the same way as before. The only differences will be:

• the last line of the Dockerfile, with the correct class and package:

ENTRYPOINT ["java", "-Djava.security.egd=file:/dev/./urandom", "-cp", "BOOT-INF/classes:BOOT-INF/lib/*", "pl.akolata.healthcheck.demo.simplemicroservice.SimpleMicroserviceApplication"]

• Docker image build & run commands

docker build . \
  --tag spring-boot-healthcheck-demo/simple-microservice:latest

docker run \
  --rm \
  --name=spring-boot-healthcheck-demo-simple-microservice \
  -p 8080:8888 \
  spring-boot-healthcheck-demo/simple-microservice:latest

Surprise!

At this point simple-microservice should fail. Why? Well, because of two things:

1. It tries to reach Config Server in the default location, which is http://localhost:8888, so inside the same container
2. the spring.cloud.config.fail-fast=true property has been set

The application logs should look more or less like these ones:

[main] ERROR org.springframework.boot.SpringApplication - Application run failed
org.springframework.cloud.config.client.ConfigClientFailFastException: Could not locate PropertySource and the fail fast property is set, failing
        at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.doLoad(ConfigServerConfigDataLoader.java:199)
        at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.load(ConfigServerConfigDataLoader.java:103)
        at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.load(ConfigServerConfigDataLoader.java:62)
        at org.springframework.boot.context.config.ConfigDataLoaders.load(ConfigDataLoaders.java:96)
        at org.springframework.boot.context.config.ConfigDataImporter.load(ConfigDataImporter.java:128)
        at org.springframework.boot.context.config.ConfigDataImporter.resolveAndLoad(ConfigDataImporter.java:86)
        at org.springframework.boot.context.config.ConfigDataEnvironmentContributors.withProcessedImports(ConfigDataEnvironmentContributors.java:115)
        at org.springframework.boot.context.config.ConfigDataEnvironment.processWithProfiles(ConfigDataEnvironment.java:313)
        at org.springframework.boot.context.config.ConfigDataEnvironment.processAndApply(ConfigDataEnvironment.java:234)
        at org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor.postProcessEnvironment(ConfigDataEnvironmentPostProcessor.java:96)
        at org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor.postProcessEnvironment(ConfigDataEnvironmentPostProcessor.java:89)
        at org.springframework.boot.env.EnvironmentPostProcessorApplicationListener.onApplicationEnvironmentPreparedEvent(EnvironmentPostProcessorApplicationListener.java:109)
        at org.springframework.boot.env.EnvironmentPostProcessorApplicationListener.onApplicationEvent(EnvironmentPostProcessorApplicationListener.java:94)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131)
        at org.springframework.boot.context.event.EventPublishingRunListener.multicastInitialEvent(EventPublishingRunListener.java:136)
        at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:81)
        at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:64)
        at java.base/java.lang.Iterable.forEach(Unknown Source)
        at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:118)
        at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:112)
        at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:63)
        at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:352)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1291)
        at pl.akolata.healthcheck.demo.simplemicroservice.SimpleMicroserviceApplication.main(SimpleMicroserviceApplication.java:10)
Caused by: org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://localhost:8888/simple-microservice/default": Connection refused
        at org.springframework.web.client.RestTemplate.createResourceAccessException(RestTemplate.java:888)
        at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:868)
        at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:764)
        at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:646)
        at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.getRemoteEnvironment(ConfigServerConfigDataLoader.java:304)
        at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.doLoad(ConfigServerConfigDataLoader.java:119)
        ... 28 common frames omitted
Caused by: java.net.ConnectException: Connection refused
        at java.base/sun.nio.ch.Net.pollConnect(Native Method)
        at java.base/sun.nio.ch.Net.pollConnectNow(Unknown Source)
        at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(Unknown Source)
        at java.base/sun.nio.ch.NioSocketImpl.connect(Unknown Source)
        at java.base/java.net.Socket.connect(Unknown Source)
        at java.base/sun.net.NetworkClient.doConnect(Unknown Source)
        at java.base/sun.net.www.http.HttpClient.openServer(Unknown Source)
        at java.base/sun.net.www.http.HttpClient.openServer(Unknown Source)
        at java.base/sun.net.www.http.HttpClient.<init>(Unknown Source)
        at java.base/sun.net.www.http.HttpClient.New(Unknown Source)
        at java.base/sun.net.www.http.HttpClient.New(Unknown Source)
        at java.base/sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)
        at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(Unknown Source)
        at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
        at java.base/sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)
        at org.springframework.http.client.SimpleBufferingClientHttpRequest.executeInternal(SimpleBufferingClientHttpRequest.java:75)
        at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48)
        at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:66)
        at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:862)
        ... 32 common frames omitted

Docker-compose (first attempt)

Let’s try to use the depends_on mechanism of Docker Compose, using a short syntax:

version: '3.9'

services:
  config-service:
    container_name: spring-boot-healthcheck-demo-config-service
    pull_policy: always
    image: spring-boot-healthcheck-demo/config-service:latest
    ports:
      - "8888:8888"
    networks:
      backend:
        aliases:
          - "config-server"

simple-microservice:
    container_name: spring-boot-healthcheck-demo-simple-microservice
    image: spring-boot-healthcheck-demo/simple-microservice:latest
    pull_policy: always
    environment:
      SERVER_PORT: 8080
      SPRING_CONFIG_IMPORT: "optional:configserver:http://config-service:8888"
    depends_on:
      - config-service
    networks:
      backend:
        aliases:
          - "simple-microservice"

networks:
  backend:
    driver: bridge

Unfortunately, this will also fail. Let’s take a look at the logs:

docker-compose up
Starting spring-boot-healthcheck-demo-config-service ... done
Creating spring-boot-healthcheck-demo-simple-microservice ... done
Attaching to spring-boot-healthcheck-demo-config-service, spring-boot-healthcheck-demo-simple-microservice
spring-boot-healthcheck-demo-config-service | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-simple-microservice | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-config-service | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-simple-microservice | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-config-service | 
spring-boot-healthcheck-demo-config-service |   .   ____          _            __ _ _
spring-boot-healthcheck-demo-config-service |  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
spring-boot-healthcheck-demo-config-service | ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
spring-boot-healthcheck-demo-config-service |  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
spring-boot-healthcheck-demo-config-service |   '  |____| .__|_| |_|_| |_\__, | / / / /
spring-boot-healthcheck-demo-config-service |  =========|_|==============|___/=/_/_/_/
spring-boot-healthcheck-demo-config-service |  :: Spring Boot ::                (v2.7.8)
spring-boot-healthcheck-demo-config-service | 
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:37.211  INFO 1 --- [           main] p.a.h.d.c.ConfigServerApplication        : Starting ConfigServerApplication using Java 17.0.6 on 7888840625df with PID 1 (/app/BOOT-INF/classes started by spring in /app)
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:37.216  INFO 1 --- [           main] p.a.h.d.c.ConfigServerApplication        : The following 1 profile is active: "native"
spring-boot-healthcheck-demo-simple-microservice | 22:41:37.801 [main] ERROR org.springframework.boot.SpringApplication - Application run failed
spring-boot-healthcheck-demo-simple-microservice | org.springframework.cloud.config.client.ConfigClientFailFastException: Could not locate PropertySource and the fail fast property is set, failing
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.doLoad(ConfigServerConfigDataLoader.java:199)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.load(ConfigServerConfigDataLoader.java:103)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.load(ConfigServerConfigDataLoader.java:62)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataLoaders.load(ConfigDataLoaders.java:96)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataImporter.load(ConfigDataImporter.java:128)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataImporter.resolveAndLoad(ConfigDataImporter.java:86)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataEnvironmentContributors.withProcessedImports(ConfigDataEnvironmentContributors.java:115)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataEnvironment.processWithProfiles(ConfigDataEnvironment.java:313)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataEnvironment.processAndApply(ConfigDataEnvironment.java:234)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor.postProcessEnvironment(ConfigDataEnvironmentPostProcessor.java:96)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor.postProcessEnvironment(ConfigDataEnvironmentPostProcessor.java:89)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.env.EnvironmentPostProcessorApplicationListener.onApplicationEnvironmentPreparedEvent(EnvironmentPostProcessorApplicationListener.java:109)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.env.EnvironmentPostProcessorApplicationListener.onApplicationEvent(EnvironmentPostProcessorApplicationListener.java:94)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.event.EventPublishingRunListener.multicastInitialEvent(EventPublishingRunListener.java:136)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:81)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:64)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/java.lang.Iterable.forEach(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:118)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:112)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:63)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:352)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplication.run(SpringApplication.java:303)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.boot.SpringApplication.run(SpringApplication.java:1291)
spring-boot-healthcheck-demo-simple-microservice |      at pl.akolata.healthcheck.demo.simplemicroservice.SimpleMicroserviceApplication.main(SimpleMicroserviceApplication.java:10)
spring-boot-healthcheck-demo-simple-microservice | Caused by: org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://config-service:8888/simple-microservice/default": Connection refused
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.web.client.RestTemplate.createResourceAccessException(RestTemplate.java:888)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:868)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:764)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:646)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.getRemoteEnvironment(ConfigServerConfigDataLoader.java:304)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.cloud.config.client.ConfigServerConfigDataLoader.doLoad(ConfigServerConfigDataLoader.java:119)
spring-boot-healthcheck-demo-simple-microservice |      ... 28 common frames omitted
spring-boot-healthcheck-demo-simple-microservice | Caused by: java.net.ConnectException: Connection refused
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.nio.ch.Net.pollConnect(Native Method)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.nio.ch.Net.pollConnectNow(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.nio.ch.NioSocketImpl.timedFinishConnect(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.nio.ch.NioSocketImpl.connect(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/java.net.Socket.connect(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.NetworkClient.doConnect(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.http.HttpClient.openServer(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.http.HttpClient.openServer(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.http.HttpClient.<init>(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.http.HttpClient.New(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.http.HttpClient.New(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at java.base/sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.http.client.SimpleBufferingClientHttpRequest.executeInternal(SimpleBufferingClientHttpRequest.java:75)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.http.client.AbstractBufferingClientHttpRequest.executeInternal(AbstractBufferingClientHttpRequest.java:48)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.http.client.AbstractClientHttpRequest.execute(AbstractClientHttpRequest.java:66)
spring-boot-healthcheck-demo-simple-microservice |      at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:862)
spring-boot-healthcheck-demo-simple-microservice |      ... 32 common frames omitted
spring-boot-healthcheck-demo-simple-microservice exited with code 1
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:39.003  INFO 1 --- [           main] o.s.cloud.context.scope.GenericScope     : BeanFactory id=7ea18433-9846-316d-934a-7954a98ecc3c
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:39.328  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8888 (http)
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:39.339  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:39.339  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.71]
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:39.450  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:39.450  INFO 1 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1639 ms
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:40.332  INFO 1 --- [           main] o.s.b.a.e.web.EndpointLinksResolver      : Exposing 2 endpoint(s) beneath base path '/actuator'
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:40.373  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8888 (http) with context path ''
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:41:40.395  INFO 1 --- [           main] p.a.h.d.c.ConfigServerApplication        : Started ConfigServerApplication in 3.729 seconds (JVM running for 4.145)

So:

• we had the depends_on instruction, and…
• config-server actually started first, but…
• was not ready yet (look at the last line: Started ConfigServerApplication in)… and
• simple-microservice had already failed

Docker-compose (working attempt)

I did the following steps:

• configured Docker Compose, how to perform a health check on these images
• used Spring Boot Actuator /readiness probe for it
• configured depends_on using the long syntax this time

version: '3.9'

services:
  config-service:
    container_name: spring-boot-healthcheck-demo-config-service
    pull_policy: always
    image: spring-boot-healthcheck-demo/config-service:latest
    ports:
      - "8888:8888"
    healthcheck:
      test: "curl --fail --silent localhost:8888/actuator/health/readiness | grep UP || exit 1"
      interval: 2s
      timeout: 3s
      retries: 5
      start_period: 2s
    networks:
      backend:
        aliases:
          - "config-server"

simple-microservice:
    container_name: spring-boot-healthcheck-demo-simple-microservice
    image: spring-boot-healthcheck-demo/simple-microservice:latest
    pull_policy: always
    healthcheck:
      test: "curl --fail --silent localhost:8080/actuator/health/readiness | grep UP || exit 1"
      interval: 2s
      timeout: 3s
      retries: 5
      start_period: 2s
    environment:
      SERVER_PORT: 8080
      SPRING_CONFIG_IMPORT: "optional:configserver:http://config-service:8888"
    depends_on:
      config-service:
        condition: service_healthy
    networks:
      backend:
        aliases:
          - "simple-microservice"

networks:
  backend:
    driver: bridge

Voila! Now it works!

Creating network "spring-boot-docker-healthcheck-demo_backend" with driver "bridge"
Creating spring-boot-healthcheck-demo-config-service ... done
Creating spring-boot-healthcheck-demo-simple-microservice ... done
Attaching to spring-boot-healthcheck-demo-config-service, spring-boot-healthcheck-demo-simple-microservice
spring-boot-healthcheck-demo-simple-microservice | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-config-service | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-simple-microservice | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-config-service | NOTE: Picked up JDK_JAVA_OPTIONS: -Xms256m -Xmx512m
spring-boot-healthcheck-demo-config-service | 
spring-boot-healthcheck-demo-config-service |   .   ____          _            __ _ _
spring-boot-healthcheck-demo-config-service |  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
spring-boot-healthcheck-demo-config-service | ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
spring-boot-healthcheck-demo-config-service |  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
spring-boot-healthcheck-demo-config-service |   '  |____| .__|_| |_|_| |_\__, | / / / /
spring-boot-healthcheck-demo-config-service |  =========|_|==============|___/=/_/_/_/
spring-boot-healthcheck-demo-config-service |  :: Spring Boot ::                (v2.7.8)
spring-boot-healthcheck-demo-config-service | 
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:16.587  INFO 1 --- [           main] p.a.h.d.c.ConfigServerApplication        : Starting ConfigServerApplication using Java 17.0.6 on f937eaa1f922 with PID 1 (/app/BOOT-INF/classes started by spring in /app)
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:16.590  INFO 1 --- [           main] p.a.h.d.c.ConfigServerApplication        : The following 1 profile is active: "native"
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:17.776  INFO 1 --- [           main] o.s.cloud.context.scope.GenericScope     : BeanFactory id=7ea18433-9846-316d-934a-7954a98ecc3c
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:18.098  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8888 (http)
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:18.108  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:18.108  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.71]
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:18.214  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:18.214  INFO 1 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1562 ms
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:19.146  INFO 1 --- [           main] o.s.b.a.e.web.EndpointLinksResolver      : Exposing 2 endpoint(s) beneath base path '/actuator'
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:19.203  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8888 (http) with context path ''
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:19.228  INFO 1 --- [           main] p.a.h.d.c.ConfigServerApplication        : Started ConfigServerApplication in 3.208 seconds (JVM running for 3.802)
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:19.657  INFO 1 --- [nio-8888-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:19.657  INFO 1 --- [nio-8888-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:19.659  INFO 1 --- [nio-8888-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 2 ms
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:21.400  INFO 1 --- [nio-8888-exec-2] o.s.c.c.s.e.NativeEnvironmentRepository  : Adding property source: Config resource 'class path resource [config/simple-microservice.yml]' via location 'classpath:/config/'
spring-boot-healthcheck-demo-config-service | 2023-01-29 22:48:21.474  INFO 1 --- [nio-8888-exec-3] o.s.c.c.s.e.NativeEnvironmentRepository  : Adding property source: Config resource 'class path resource [config/simple-microservice.yml]' via location 'classpath:/config/'
spring-boot-healthcheck-demo-simple-microservice | 
spring-boot-healthcheck-demo-simple-microservice |   .   ____          _            __ _ _
spring-boot-healthcheck-demo-simple-microservice |  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
spring-boot-healthcheck-demo-simple-microservice | ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
spring-boot-healthcheck-demo-simple-microservice |  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
spring-boot-healthcheck-demo-simple-microservice |   '  |____| .__|_| |_|_| |_\__, | / / / /
spring-boot-healthcheck-demo-simple-microservice |  =========|_|==============|___/=/_/_/_/
spring-boot-healthcheck-demo-simple-microservice |  :: Spring Boot ::                (v3.0.2)
spring-boot-healthcheck-demo-simple-microservice | 
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:21.611Z  INFO 1 --- [           main] p.a.h.d.s.SimpleMicroserviceApplication  : Starting SimpleMicroserviceApplication using Java 17.0.6 with PID 1 (/app/BOOT-INF/classes started by spring in /app)
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:21.614Z  INFO 1 --- [           main] p.a.h.d.s.SimpleMicroserviceApplication  : No active profile set, falling back to 1 default profile: "default"
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:21.661Z  INFO 1 --- [           main] o.s.c.c.c.ConfigServerConfigDataLoader   : Fetching config from server at : http://config-service:8888
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:21.661Z  INFO 1 --- [           main] o.s.c.c.c.ConfigServerConfigDataLoader   : Located environment: name=simple-microservice, profiles=[default], label=null, version=null, state=null
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:21.661Z  INFO 1 --- [           main] o.s.c.c.c.ConfigServerConfigDataLoader   : Fetching config from server at : http://config-service:8888
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:21.662Z  INFO 1 --- [           main] o.s.c.c.c.ConfigServerConfigDataLoader   : Located environment: name=simple-microservice, profiles=[default], label=null, version=null, state=null
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:22.408Z  INFO 1 --- [           main] o.s.cloud.context.scope.GenericScope     : BeanFactory id=49a25eee-6804-3b6a-b244-29bc17e80bd9
spring-boot-healthcheck-demo-simple-microservice | 2023-01-29T22:48:22.827Z  INFO 1 --- [           main] p.a.h.d.s.SimpleMicroserviceApplication  : Started SimpleMicroserviceApplication in 2.162 seconds (process running for 2.544)
spring-boot-healthcheck-demo-simple-microservice exited with code 0

As you can see, all the login lines at the beginning come from spring-boot-healthcheck-demo-config-service container, and after the Started ConfigServerApplication line you can see the login lines from the spring-boot-healthcheck-demo-simple-microservice container.

Summary

In this article I described how to:

• use Spring Actuator and its probes to check if a service is ready
• use the long Docker Compose depends_on syntax and describe dependencies using condition
• control the run order of containers and conditions in Docker Compose

You can always use tools like jq to parse Actuator responses, or add your own Actuator endpoint. There are also additional options for configuring health checks, such as interval, etc. If you don’t want to describe health checks in the Compose file, you can also use the HEALTHCHECK instruction inside the Dockerfile. Thanks for reading!

References:

• GitHub repository: https://github.com/akolata/spring-boot-actuator-docker-health-check
• https://docs.docker.com/engine/reference/builder/#healthcheck
• https://docs.docker.com/compose/startup-order/
• https://docs.docker.com/compose/compose-file/compose-file-v3/#healthcheck
• https://docs.docker.com/compose/compose-file/compose-file-v3/#depends_on
• https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes
• https://docs.spring.io/spring-boot/docs/current/reference/html/actuator.html#actuator.endpoints.kubernetes-probes
• https://spring.io/guides/gs/spring-boot-docker/

Words by Aleksander Kołata, Senior Full Stack Developer

https://www.linkedin.com/in/aleksander-kolata/

Editing by Kinga Kuśnierz, Content Writer

https://www.linkedin.com/in/kingakusnierz/