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Docker Compose Configuration Cheatsheet

Health Check

The healthcheck directive allows you to specify a command that Docker will run to check the health of your container. If the command returns a non-zero code, Docker will consider the container to be unhealthy.

  • Docker will run the test command to check the health of your container. In this case, we used the cqlsh command to describe the keyspaces in Cassandra.
  • The interval setting specifies how often Docker should run the healthcheck command.
  • The timeout setting specifies how long Docker should wait for the healthcheck command to complete.
  • The retries setting specifies how many times Docker should run the healthcheck command before giving up and killing the container.

Example:

healthcheck:
  test: [ "CMD", "cqlsh", "-e", "describe keyspaces" ]
  interval: 5s
  timeout: 5s
  retries: 60

Restart Policy

This will ensure that your service automatically restarts if it crashes or if the Docker daemon restarts.

restart: unless-stopped
restart: always

Logging

Docker Compose supports logging configuration which can be useful for debugging and monitoring. You can specify a driver (json-file, syslog, etc.) and options depending on your needs.

logging:
  driver: "json-file"
  options:
    max-size: "200k"
    max-file: "10"

The logging configuration is set to use the json-file driver and will rotate logs when they reach 200k in size, keeping a maximum of 10 log files.

Resource Limits

Limit resources like CPU and memory. It's not strictly required, but it's better to have some limits.

mem_limit: "${MEM_LIMIT}"
cpus: "${CPU_LIMIT}"

Networking

Bridge driver is the default network driver for Docker, and it's used when you don't specify a driver. It provides a private network internal to the host so containers on this network can communicate.

networks:
  my_network:
    driver: bridge

By default, all containers have networking enabled and they can make any outgoing connections. The operator can completely disable networking with docker run --network none which disables all incoming and outgoing networking. In cases like this, you would perform I/O through files or STDIN and STDOUT only.

Update Strategy

For services that need to be updated with zero downtime, specify an update strategy.

deploy:
  mode: replicated
  replicas: 1
  update_config:
    parallelism: 1
    delay: 10s

The update configuration ensures that updates are carried out one at a time with a delay of 10s between updates.

Last update: May 6, 2024