Replaces our current host-based HTTP healthchecks with Docker
healthchecks, and adds a new `healthcheck.cmd` config option that can be
used to define a custom health check command. Also removes Traefik's
healthchecks, since they are no longer necessary.
When deploying a container that has a healthcheck defined, we wait for
it to report a healthy status before stopping the old container that it
replaces. Containers that don't have a healthcheck defined continue to
wait for `MRSK.config.readiness_delay`.
There are some pros and cons to using Docker healthchecks rather than
checking from the host. The main advantages are:
- Supports non-HTTP checks, and app-specific check scripts provided by a
container.
- When booting a container, allows MRSK to wait for a container to be
healthy before shutting down the old container it replaces. This
should be safer than relying on a timeout.
- Containers with healthchecks won't be active in Traefik until they
reach a healthy state, which prevents any traffic from being routed to
them before they are ready.
The main _disadvantage_ is that containers are now required to provide
some way to check their health. Our default check assumes that `curl` is
available in the container which, while common, won't always be the
case.
The Healthcheck container is shut down right after performing the check, this
makes it harder to troubleshoot configuration issues in the healthcheck
endpoint, e.g DNS rebinding error. Printing the container logs helps the troubleshooting.
Match word
Language
Suggest what accessories are
There are also accessories
Default already shown
Better example
Warn about secrets being shown
Now also accessories
Wording
Clarifications
Clarify how to see options
General option for all
Options important here too
Hide subcommands
Implied
Simpler as just version
Be concise
Missing word
Wordsmith
Simpler and uniform words are better
Clarify what exactly we're manipulating
Wordsmithing
Implicit
Simpler language
Hide subcommands
Clarify its container management
Just one per server
Simpler
