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A simple script to wait for other docker images to be started while using docker-compose
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docker-compose-wait

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A small command line utility to wait for other docker images to be started while using docker-compose. It permits to wait for a fixed amount of seconds and/or to wait until a TCP port is open on a target image.

Usage

This utility should be used in docker build process and launched before your application starts.

For example, your application "MySuperApp" uses MongoDB, Postgres and MySql (wow!) and you want to be sure that when it starts all other systems are available, then simply customize your dockerfile this way:

FROM alpine

## Add your application to the docker image
ADD MySuperApp.sh /MySuperApp.sh

## Add the wait script to the image
ADD https://github.com/ufoscout/docker-compose-wait/releases/download/2.5.0/wait /wait
RUN chmod +x /wait

## Launch the wait tool and then your application
CMD /wait && /MySuperApp.sh

Done! the image is ready.

Now let's modify the docker-compose.yml file:

version: "3"

services:

  mongo:
    image: mongo:3.4
    hostname: mongo
    ports:
      - "27017:27017"

  postgres:
    image: "postgres:9.4"
    hostname: postgres
    ports:
      - "5432:5432"

  mysql:
    image: "mysql:5.7"
    hostname: mysql
    ports:
      - "3306:3306"

  mySuperApp:
    image: "mySuperApp:latest"
    hostname: mySuperApp
    environment:
      WAIT_HOSTS: postgres:5432, mysql:3306, mongo:27017

When docker-compose is started (or Kubernetes or docker stack or whatever), your application will be started only when all the pairs host:port in the WAIT_HOSTS variable are available. The WAIT_HOSTS environment variable is not mandatory, if not declared, the script executes without waiting.

If you want to use the script directly in docker-compose.yml instead of the Dockerfile, please note that the command: configuration option is limited to a single command so you should wrap in a sh call. For example:

command: sh -c "/wait && /MySuperApp.sh"

This is discussed further here and here.

Additional configuration options

The behaviour of the wait utility can be configured with the following environment variables:

  • WAIT_HOSTS: comma separated list of pairs host:port for which you want to wait.
  • WAIT_HOSTS_TIMEOUT: max number of seconds to wait for the hosts to be available before failure. The default is 30 seconds.
  • WAIT_BEFORE_HOSTS: number of seconds to wait (sleep) before start checking for the hosts availability
  • WAIT_AFTER_HOSTS: number of seconds to wait (sleep) once all the hosts are available
  • WAIT_SLEEP_INTERVAL: number of seconds to sleep between retries. The default is 1 second.

Notes

This utility was explicitly written to be used with docker-compose; however, it can be used everywhere since it has no dependencies on docker.

Version 2.0.0 was rewritten from scratch in rust. One of the many positive consequences is that it does not rely on external tools (e.g netcat) as the previous versions.

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