Where the `application` is the internal application name, same as previously used in the package name, `subdomain` is the subdomain on which the application will be accessible and the `admin-username` and `admin-password` are optional admin credentials created by `install.sh` during the application setup. These parameters will show up as part of the application definition in `/etc/vmmgr/conf.json` and will be visible / usable via web GUI.
### unregister-app
Counterpart to `register-app`. This hook is invoked by `uninstall.sh` and simply removes the application definition from `/etc/vmmgr/conf.json`, rendering it invisible / unusable via web GUI, which is expected as part of the uninstallation process. It is invoked as
```
vmmgr unregister-app <application>
```
Where the `application` is the internal application name, same as previously used in the package name.
LXC hooks set various environment variables prior to calling the defined executables. For overview of native LXC hooks, see section *Container hooks* in the official [lxc.container.conf(5) documentation](https://linuxcontainers.org/lxc/manpages/man5/lxc.container.conf.5.html). All hooks mentioned in this chapter are hardcoded in the container configuration via a template used by[`lxcbuild`](lxcbuild).
This hook is invoked by LXC's `lxc.hook.pre-start`, which is called in host environment (i.e. in the virtual machine, not in the container) before the container's ttys, consoles or mounts are up. This hook removes the contents of container's ephemeral OverlayFS layer in case of previous unclean container shutdown. Then calls application's `update-conf.sh` script (if it is present) with environment variables populated from configuration in `/etc/vmmgr/conf.json`, allowing for the correct configuration of application in components which are not part of the currently starting container, e.g. application URL in a database or persistent configuration file. It is invoked as
```
vmmgr lxc-container
```
The hook expects the `LXC_NAME` environment variable to be populated.
### register-container
This hook is invoked by LXC's `lxc.hook.start-host` which is called in host environment (i.e. in the virtual machine, not in the container) after the container has been setup, immediately before launching the container's init process. This hook sets up a container's network settings (IP address, netmask, default route). The network settings is managed via *poor man's DHCP server*, which simply assigns the first unassigned IP address from range 172.17.0.0/16 and holds the lease table in hosts's `/etc/hosts` which is also mounted in all containers, keeping the network settings consistent across all container stop / starts. The hook is invoked as
```
vmmgr register-container
```
The hook expects `LXC_NAME` and `LXC_PID` environment variables to be populated, so it can record the value of `LXC_NAME` into `/etc/hosts` leases and then `nsenter` the container namespace via `LXC_PID` and set the leased address.
### unregister-container
This hook is invoked by LXC's `lxc.hook.post-stop` which is called in host environment (i.e. in the virtual machine, not in the container) after the container has been shut down. This hook releases the IP address leased by `register-container` and then removes the contents of container's ephemeral OverlayFS layer. It is invoked as
```
vmmgr unregister-container
```
The hook expects the `LXC_NAME` environment variable to be populated.
## Init hooks
### rebuild-issue
This hook is called by `/sbin/vmtty`, which is the default *login program* used by `/sbin/getty` defined in `/etc/inittab`. This tty contains a banner with branding, legal notice and information about VM network settings and URL, stored in `/etc/issue`. The URL needs to be generated based on the settings in `/etc/vmmgr/conf.json`, which is exactly what this hook does. On every invocation, it regenerates the contents of `/etc/issue` with up-to-date information. The hook is invoked as-is with no parameters or environment variables.
```
vmmgr rebuild-issue
```
### register-proxy
This hook is invoked by `/etc/init.d/<application>` OpenRC init script as part of `start_post()` function. It is invoked as
```
vmmgr register-proxy <application>
```
The hook creates HTTP proxy configuration file for VM's nginx HTTP server for the given `application`, based on the settings in `/etc/vmmgr/conf.json`. Then it reloads the nginx service to take the configuration into effect. The proxy configuration requires a valid IP/hostname in `/etc/hosts`, which exists only after the container has been started and `register-container` hook called, hence the post-start invocation.
### unregister-proxy
Counterpart to `register-proxy`. This hook is called by `/etc/init.d/<application>` OpenRC init script as part of `stop_pre()` function. It is invoked as
```
vmmgr unregister-proxy <application>
```
The hook simply removes the configuration file for VM's nginx HTTP server for the given `application` and reloads the nginx service to take the configuration out of effect.
