Adds support for maintenance mode to Kamal.
There are two new commands:
- `kamal app maintenance` - puts the app in maintenance mode
- `kamal app live` - puts the app back in live mode
In maintenance mode, the kamal proxy will respond to requests with a
503 status code. It will use an error page built into kamal proxy.
You can use your own error page by setting `error_pages_path` in the
configuration. This will copy any 4xx.html or 5xx.html files from that
page to a volume mounted into the proxy container.
Add two new hooks pre-app-boot and post-app-boot. They are analagous
to the pre/post proxy reboot hooks.
If the boot strategy deploys in groups, then the hooks are called once
per group of hosts and `KAMAL_HOSTS` contains a comma delimited list of
the hosts in that group.
If all hosts are deployed to at once, then they are called once with
`KAMAL_HOSTS` containing all the hosts.
It is possible to have pauses between groups of hosts in the boot config,
where this is the case the pause happens after the post-app-boot hook is
called.
Add commands for managing proxy boot config. Since the proxy can be
shared by multiple applications, the configuration doesn't belong in
`config/deploy.yml`.
Instead you can set the config with:
```
Usage:
kamal proxy boot_config <set|get|clear>
Options:
[--publish], [--no-publish], [--skip-publish] # Publish the proxy ports on the host
# Default: true
[--http-port=N] # HTTP port to publish on the host
# Default: 80
[--https-port=N] # HTTPS port to publish on the host
# Default: 443
[--docker-options=option=value option2=value2] # Docker options to pass to the proxy container
```
By default we boot the proxy with `--publish 80:80 --publish 443:443`.
You can stop it from publishing ports, specify different ports and pass
other docker options.
The config is stored in `.kamal/proxy/options` as arguments to be passed
verbatim to docker run.
Where someone wants to set the options in their application they can do
that by calling `kamal proxy boot_config set` in a pre-deploy hook.
There's an example in the integration tests showing how to use this to
front kamal-proxy with Traefik, using an accessory.
Rather than waiting 5 seconds and hoping for the best after we boot
docker compose, add docker healthchecks and wait for all the containers
to be healthy.
