### Best Approach - Resilient App Starts

While docker *does* support startup dependencies, they officially recommend updating your app start logic to test for the availability of external dependencies and retry.  This has lots of benefits for robust applications that may restart in the wild on the fly in addition to circumventing the race condition in `docker compose up`

### `depends_on` & `service_healthy` - Compose 1.27.0<sup>+</sup>

`depends_on` is back in docker compose v1.27.0+ (was deprecated in v3) in the [Compose Specification](https://docs.docker.com/compose/compose-file/#depends_on)


Each service should also implement a `service_healthy` check to be able to report if it's fully setup and ready for downstream dependencies.

```yml
version: '3.0'
services:
  php:
    build:
      context: .
      dockerfile: tests/Docker/Dockerfile-PHP
    depends_on:
      redis:
        condition: service_healthy
  redis:
    image: redis
    healthcheck:
      test: ["CMD", "redis-cli", "ping"]
      interval: 1s
      timeout: 3s
      retries: 30
```


### `wait-for-it.sh`

The recommended approach from docker according to their docs on [Control startup and shutdown order in Compose][1] is to download [`wait-for-it.sh`][0] which takes in the `domain:port` to poll and then executes the next set of commands if successful.  

```yml
version: "2"
services:
  web:
    build: .
    ports:
      - "80:8000"
    depends_on:
      - "db"
    command: ["./wait-for-it.sh", "db:5432", "--", "python", "app.py"]
  db:
    image: postgres
```


**Note**: This requires overriding the startup command of the image, so make sure you know what wanted to pass to maintain parity of the default startup.


### Further Reading

* [Docker Compose wait for container X before starting Y][2]
* [Difference between links and depends_on in docker_compose.yml][3]
* [How can I wait for a docker container to be up and running?][4]
* [Docker Compose Wait til dependency container is fully up before launching][5]
* [depends_on doesn't wait for another service in docker-compose 1.22.0][6]

[0]: https://github.com/vishnubob/wait-for-it/blob/master/wait-for-it.sh
[1]: https://docs.docker.com/compose/startup-order/
[2]: https://stackoverflow.com/q/31746182/1366033
[3]: https://stackoverflow.com/q/35832095/1366033
[4]: https://stackoverflow.com/q/21183088/1366033
[5]: https://stackoverflow.com/q/55502234/1366033
[6]: https://stackoverflow.com/q/52699899/1366033

I have the following **docker-compose**, where I need to wait for the service **jhipster-registry** to be up and accepting connections before starting **myprogram-app**.

I tried the healtcheck way, following the official doc https://docs.docker.com/compose/compose-file/compose-file-v2/ 

    version: '2.1'
    services:
        myprogram-app:
            image: myprogram
            mem_limit: 1024m
            environment:
                - SPRING_PROFILES_ACTIVE=prod,swagger
                - EUREKA_CLIENT_SERVICE_URL_DEFAULTZONE=http://admin:$${jhipster.registry.password}@jhipster-registry:8761/eureka
                - SPRING_CLOUD_CONFIG_URI=http://admin:$${jhipster.registry.password}@jhipster-registry:8761/config
                - SPRING_DATASOURCE_URL=jdbc:postgresql://myprogram-postgresql:5432/myprogram
                - JHIPSTER_SLEEP=0
                - SPRING_DATA_ELASTICSEARCH_CLUSTER_NODES=myprogram-elasticsearch:9300
                - JHIPSTER_REGISTRY_PASSWORD=53bqDrurQAthqrXG
                - EMAIL_USERNAME
                - EMAIL_PASSWORD
            ports:
                - 8080:8080
            networks:
              - backend
            depends_on:
              - jhipster-registry:
                  "condition": service_started
              - myprogram-postgresql
              - myprogram-elasticsearch
        myprogram-postgresql:
            image: postgres:9.6.5
            mem_limit: 256m
            environment:
                - POSTGRES_USER=myprogram
                - POSTGRES_PASSWORD=myprogram
            networks:
              - backend
        myprogram-elasticsearch:
            image: elasticsearch:2.4.6
            mem_limit: 512m
            networks:
              - backend
        jhipster-registry:
            extends:
                file: jhipster-registry.yml
                service: jhipster-registry
            mem_limit: 512m
            ports:
                - 8761:8761
            networks:
              - backend
            healthcheck:
              test: "exit 0"
    networks:
      backend:
        driver: "bridge"

but I get the following error when running `docker-compose up`:

    ERROR: The Compose file './docker-compose.yml' is invalid because:
    services.myprogram-app.depends_on contains {"jhipster-registry": {"condition": "service_started"}}, which is an invalid type, it should be a string

Am I doing something wrong, or this feature is no more supported? How to achieve this sync between services?

**Updated version**

    version: '2.1'
    services:
        myprogram-app:
            image: myprogram
            mem_limit: 1024m
            environment:
                - SPRING_PROFILES_ACTIVE=prod,swagger
                - EUREKA_CLIENT_SERVICE_URL_DEFAULTZONE=http://admin:$${jhipster.registry.password}@jhipster-registry:8761/eureka
                - SPRING_CLOUD_CONFIG_URI=http://admin:$${jhipster.registry.password}@jhipster-registry:8761/config
                - SPRING_DATASOURCE_URL=jdbc:postgresql://myprogram-postgresql:5432/myprogram
                - JHIPSTER_SLEEP=0
                - SPRING_DATA_ELASTICSEARCH_CLUSTER_NODES=myprogram-elasticsearch:9300
                - JHIPSTER_REGISTRY_PASSWORD=53bqDrurQAthqrXG
                - EMAIL_USERNAME
                - EMAIL_PASSWORD
            ports:
                - 8080:8080
            networks:
              - backend
            depends_on:
              jhipster-registry:
                condition: service_healthy
              myprogram-postgresql:
                condition: service_started
              myprogram-elasticsearch:
                condition: service_started
            #restart: on-failure
        myprogram-postgresql:
            image: postgres:9.6.5
            mem_limit: 256m
            environment:
                - POSTGRES_USER=myprogram
                - POSTGRES_PASSWORD=tuenemreh
            networks:
              - backend
        myprogram-elasticsearch:
            image: elasticsearch:2.4.6
            mem_limit: 512m
            networks:
              - backend
        jhipster-registry:
            extends:
                file: jhipster-registry.yml
                service: jhipster-registry
            mem_limit: 512m
            ports:
                - 8761:8761
            networks:
              - backend
            healthcheck:
              test: ["CMD", "curl", "-f", "http://jhipster-registry:8761", "|| exit 1"]
              interval: 30s
              retries: 20
              #start_period: 30s
    networks:
      backend:
        driver: "bridge"

The updated version gives me a different error, 

    ERROR: for myprogram-app  Container "8ebca614590c" is unhealthy.
    ERROR: Encountered errors while bringing up the project.

saying that the container of jhipster-registry is unhealthy, but it's reachable via browser. How can I fix the command in the healthcheck to make it work?