Updated docker-tcp.md

content/posts/docker-tcp.md

@@ -65,7 +65,7 @@ In the above snippet, replace `<HOST>` with the hostname (output of the
 `hostname` command) of the machine who's API you want to expose. Now we've
 created `server-key.pem` and `server.csr`.
 
-As a final step, we need to create a file named `extfile.cnf` with the
+After this, we need to create a file named `extfile.cnf` with the
 following content:
 
 ```
@@ -75,3 +75,87 @@ extendedKeyUsage = serverAuth
 
 Here, we once again replace `<HOST>` with the machine's hostname, and `<IP>`
 with the machine's public IP.
+
+This file can now be used to generate the actual signed certificate:
+
+```shell
+openssl x509 -req -days 365 -sha256 -in server.csr -CA ca.pem -CAkey \
+    ca-key.pem -CAcreateserial -out server-cert.pem -extfile extfile.cnf
+```
+
+Here, we can once again change the days argument to the value we want. After
+all these steps, we're left with a signed server-side certificate.
+
+## Client-side
+
+Now we'll generate the client-side certificates. We start by creating a `csr`
+file:
+
+```shell
+openssl genrsa -out key.pem 4096
+openssl req -subj '/CN=client' -new -key key.pem -out client.csr
+```
+
+After this, we create another `.cnf`, this time to configure the client-side
+keys. Add this to a file named `extfile-client.cnf`:
+
+```
+extendedKeyUsage = clientAuth
+```
+
+And then, we generate the client-side key:
+
+```
+openssl x509 -req -days 365 -sha256 -in client.csr -CA ca.pem -CAkey \
+    ca-key.pem -CAcreateserial -out cert.pem -extfile extfile-client.cnf
+```
+
+Once again change the days value to whatever you want. Now we're left with all
+the files we need to securely expose the API.
+
+## Exposing the API
+
+**Note**: the following steps will restart the Docker engine and all
+running containers, so make sure this won't break anything.
+
+Start by creating a directory on the host that you're not going to delete. In
+the following steps, replace `<DIR>` with the absolute path to this directory.
+After this, copy `ca.pem`, `server-cert.pem` and `server-key.pem` to this
+directory.
+
+We're gonna be creating a system config file for the Docker service (this guide
+assumes the use of `systemd`). In
+`/etc/systemd/docker.service.d/startup_options.conf`, put the following:
+
+```shell
+[Service]
+ExecStart=
+ExecStart=/usr/bin/dockerd --tlsverify --tlscacert='<DIR>/ca.pem' --tlscert='<DIR>/server-cert.pem' --tlskey='<DIR>/server-key.pem' -H fd:// -H tcp://0.0.0.0:2376
+```
+
+Don't forget the replace `<PATH>` with the path to your actual directory.
+
+The final step is restarting the Docker engine:
+
+```shell
+systemctl daemon-reload
+systemctl restart docker.service
+```
+
+**Note**: these commands require root.
+
+After all this, you should have a Docker API that's accessible using an
+encrypted connection. Let's test it by adding it to Portainer!
+
+## Adding engine to Portainer
+
+Thankfully this is the easy part. In Portainer, add a new endpoint and choose
+the "Docker" type. Pick a name for your endpoint, fill in the endpoint URL
+including the port number (Docker's default port number is `2375`) and enable
+the "TLS" switch. We choose "TLS with server and client verification", as this
+is the safest. The files to upload are `ca.pem` for the TLS CA certificate,
+`cert.pem` for the TLS certificate and `key.pem` for the TLS key. If all goes
+well, you should now connect to the host!
+
+Now, I know these steps can be quite tedious to repeat, so I've written
+[a script](/scripts/docker-tcp.sh) that can automate this process for you.