Health check is a Docker feature that allows us to check the status of a Docker container. It allows us to ensure that a container has been successfully started and is working as expected.
In Docker Compose, we can use the health check feature to check the health of the services (services) we are declaring. This ensures that services are only used when they are fully started and ready to serve requests.
To use the health check in Docker Compose, we need to perform the following steps:
1. Declare the health check feature in the docker-compose.yml file:
1 2 3 4 5 6 7 8 9 10 | version <span class="token punctuation">:</span> <span class="token string">"3.8"</span> services <span class="token punctuation">:</span> myservice <span class="token punctuation">:</span> image <span class="token punctuation">:</span> myimage healthcheck <span class="token punctuation">:</span> test <span class="token punctuation">:</span> <span class="token punctuation">[</span> <span class="token string">"CMD"</span> <span class="token punctuation">,</span> <span class="token string">"curl"</span> <span class="token punctuation">,</span> <span class="token string">"-f"</span> <span class="token punctuation">,</span> <span class="token string">"http://localhost"</span> <span class="token punctuation">]</span> interval <span class="token punctuation">:</span> <span class="token number">1</span> m30s timeout <span class="token punctuation">:</span> <span class="token number">10</span> s retries <span class="token punctuation">:</span> <span class="token number">3</span> |
In the above example, we have declared a service myservice, and include the health check feature. test is the command to check the health of the service, and interval, timeout, and retries are respectively the time to wait between tests, the maximum time to execute the test, and the number of retries if the test fails. .
2. Start the service with the command:
1 2 | docker <span class="token operator">-</span> compose up |
When we run this command, Docker Compose will start the services and start checking their health. If the health check for a service fails, Docker Compose will attempt to restart the service or mark the service as unavailable.
In addition, we can also use the docker-compose ps command to see the status of services and their health check.
1 2 | docker <span class="token operator">-</span> compose ps |
This will display a list of services and their status, including the health check status.
That’s how to use the health check feature in Docker Compose. We can use this feature to ensure that our services are always working properly and serving user requests in the best way.