## Docker Swarm health check example

This example shows how health check works in Docker Swarm.

### What does this container do?

Container runs a nginx server and it also runs a script which writes a ``dead``
status to ``/usr/share/nginx/html/status`` file on every odd run which is then
picked by the health check that expects ``alive`` status from the nginx running
in the container.

So every odd run the container gets ``unhealthy`` status.
Then you can observe that running this container in Docker Engine alone will
not restart it. Hence we will run it as a service in the Docker Swarm which
will ensure the container gets restarted until it gets ``healthy`` status.

### Building image

```
docker build -t healthcheck-test .
```

### Setting up env

Make sure you have recent Docker Engine installed.

```
docker swarm init
```

### Running the service

```
docker service create \
  --name test1 \
  --mount type=bind,src=/tmp,dst=/usr/share/nginx/html \
  --detach healthcheck-test
```

### Watching the health check

```
docker ps |grep test1
docker service ls
```

### Cleaning up

```
docker service rm test1
docker swarm leave --force
rm -f -- /tmp/status
docker rmi healthcheck-test
```

### Extra

If you want to restart the container manually, you need to downscale it to 0
first and then upscale it back again.

```
docker service scale test1=0
docker service scale test1=1
```

### References

- https://docs.docker.com/compose/compose-file/
- https://docs.docker.com/engine/reference/builder/