Add documentation on monitoring Docker via TCP

This change adds documentation and an example on how to configuration the Docker Daemon to expose the TCP port and how to set up the monitoring in Uptime-Kuma.

How-to-Monitor-Docker-Containers.md

@@ -20,7 +20,45 @@ volumes:
 
 ### (Method 2) TCP - Bridge Mode
 
-TODO
+**Expose TCP port**  
+To enable TCP monitoring, you need to first expose the Docker daemon on a TCP port. The primary documentation is available [here](https://docs.docker.com/config/daemon/) but the example below provides some quick options.
+
+Update the daemon configuration located at `/etc/docker/daemon.json`:
+```json
+{
+   #any additional parameters should be kept
+
+   #Insecure option, only use this if you are running on a closed network
+   "hosts": ["unix:///var/run/docker.sock","tcp://<host IP address>:2375"]
+
+   #Secure option
+   "tls": true,
+   "tlscert": "/var/docker/server.pem",
+   "tlskey": "/var/docker/serverkey.pem",
+   "hosts": ["unix:///var/run/docker.sock","tcp://<host IP address>:2376"]
+}
+```
+
+Restart the daemon using `sudo systemctl restart docker.service`.
+
+If the daemon fails to start, it may be because there are duplicate keys, in this case hosts, -H, that is already part of the daemon configuration.
+
+You can edit the startup configuration using `sudo systemctl edit docker.service`.
+
+```toml
+[Service]
+#The blank ExecStart is required to clear the current entry point
+ExecStart=
+#Replace the existing ExecStart but only remove the properties that you have added into the daemon.json file, leave all else the same.
+ExecStart=/usr/bin/dockerd --containerd=/run/containerd/containerd.sock
+```
+
+My original ExecStart was: `ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock`, note the -H that would cause a duplicate property error.
+
+**Update uptime-kuma**  
+Add a new Docker host and choose TCP as the option. Specify the IP address of the host and the TCP port you exposed, as seen below.
+
+![Docker host monitor](img/docker-host.png)
 
 ## Related Disscussion