healthdog
=========

healthdog is a utility program that runs a healthcheck program periodically and
pets systemd's service watchdog.

Installing
----------

You can use `cargo build --release` to build this project and then copy
`./target/release/healthdog` to `/usr/local/bin/healthdog`.

Usage
-----

Let's say that we wish to run Docker and continuously monitor that the daemon
is responsive and restart in case it isn't.

First we create a program that will test the docker daemon and return **0** on
success, **1** otherwise.

* **`/usr/bin/check-docker`**:

```bash
#!/bin/sh

set -o errexit

# Check that info works
docker info > /dev/null
# Check that we can read containers from disk
docker ps > /dev/null
```

Then we prefix the `ExecStart` directive with healthdog and also set our desired `WatchdogSec` value.

* **`docker.service`**

```ini
[Unit]
Description=Docker Application Container Engine

[Service]
Type=simple
ExecStart=/usr/local/bin/healthdog --healthcheck=check-docker /usr/bin/dockerd
WatchdogSec=10
Restart=always

[Install]
WantedBy=multi-user.target
```

The service will spawn healthdog which in turn will run `check-docker` every 5
seconds (half the systemd duration) and pet the watchdog if it successfully
returns.