Started writing Docker TCP post

content/posts/docker-tcp.md

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+---
+draft: true
+title: "Encrypting a Docker API for Remote Access Using Portainer"
+date: "2021-05-16"
+---
+
+tl;dr [This script](/docker-tcp.sh) has everything you need, just run
+`./docker-tcp.sh -h` (after making it executable) for any help.
+
+## Introduction
+
+To manage my little army of servers, I use
+[Portainer CE](https://www.portainer.io/). It's an open-source management tool
+for controlling Dockerized applications across multiple hosts. It can handle
+regular Docker containers, compose stacks, Kubernetes clusters or Docker swarm
+mode. It's a really useful tool to keep track of everything, and nowadays, I
+really can't miss it.
+
+Before we can add a host to Portainer, its Docker API has to be exposed to the
+public, and in order to do this, we need to protect it using encryption (unless
+of course you like random people controlling your server). This post will
+explain how this can be done, and I've also written a script that can automate
+the "heavy" lifting.
+
+**Note**: This tutorial is only for Linux. I have no experience with managing a
+Windows server and therefore can't confirm these steps will also work on a
+Windows machine.
+
+I recommend running these commands on your local Linux machine and just copying
+the certificates to the server later, as you'll need all the files in order to
+add the host to Portainer later.
+
+## Server-side
+
+To make the connection as secure as possible, we'll use both a server- & a
+client-side certificate. This first section describes how to generate the
+former:
+
+```shell
+openssl genrsa -aes256 -out ca-key.pem 4096
+openssl req -new -x509 -days 365 -key ca-key.pem -sha256 -out ca.pem
+```
+
+These first two commands generate the
+[CA](https://en.wikipedia.org/wiki/Certificate_authority) key. You'll be asked
+for some basic information, e.g. your country, state, city, organization, etc.
+The most important one is the password. Keep this one safe, as you'll be asked
+for it later when creating the client key.
+
+One thing to note here is the `-days 365` flag. This defines after how many
+days this certificate will expire (but only when the `-x509` flag is
+specified). By default, its value is set at 30 days, but I find this to be
+rather short. After this time, you'll have to repeat these steps and generate a
+new certificate. You'll have to figure out for yourself how long you'd like
+your certificate to be valid for.
+
+Now we can generate the server key:
+
+```shell
+openssl genrsa -out server-key.pem 4096
+openssl req -subj "/CN=<HOST>" -sha256 -new -key server-key.pem -out server.csr
+```
+
+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
+following content:
+
+```
+subjectAltName = DNS:<HOST>,IP:<IP>,IP:127.0.0.1 >> extfile.cnf
+extendedKeyUsage = serverAuth
+```
+
+Here, we once again replace `<HOST>` with the machine's hostname, and `<IP>`
+with the machine's public IP.

static/docker-tcp.sh

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+#!/usr/bin/env sh
+
+# This script generates an openSSL key pair which can be used to expose a
+# Docker API over the internet.
+
+