How to view docker-compose healthcheck logs?

Inside my docker-compose.yml, I have the following service healthcheck section. I want to know if MariaDB is actually ready to handle queries. A service named cmd is configured to depend on condition: service_healthy.

  db:
    image: mariadb:10
    environment:
      MYSQL_RANDOM_ROOT_PASSWORD: 1
      MYSQL_USER: user
      MYSQL_PASSWORD: password
      MYSQL_DATABASE: database
    healthcheck:
      test: ["CMD", "mysql", "--user=user", "--password=password", "--execute='SELECT 1'", "--host=127.0.0.1", "--port=3306"]
      interval: 1s
      retries: 30

This healthcheck does not work, shows that the service is unhealthy.

How do I check the output of the test CMD?

You can use:

docker inspect --format "{{json .State.Health }}" <container name> | jq

Output:

{
    "Status": "unhealthy",
    "FailingStreak": 63,
    "Log": [
        {
            "Start": "2017-03-11T20:49:19.668895201+03:30",
            "End": "2017-03-11T20:49:19.735722044+03:30",
            "ExitCode": 1,
            "Output": "ERROR 1064 (42000) at line 1: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ''SELECT 1'' at line 1\n"
        }
    ]
}

And look for the output section.

To get the Output only:

docker inspect --format "{{json .State.Health }}" mariadb_db_1 | jq '.Log[].Output'

For swarm mode use the folling format (thanks for pointing it out @shotgunner):

{{json.Spec.TaskTemplate.ContainerSpec.Healthcheck}}

Feel free to swap jq for whatever tool you use for json pretty print.