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Posted 5 Feb 2020

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Service reloading Docker containers running web apps behind proxy after renewal of Let's Encrypt certificates managed by Certbot

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5 Feb 2020MIT3 min read
Service unit for auto reloading Docker containers running web apps behind nginx reverse proxy server after renewal of Let's Encrypt certificates managed by Certbot on Linux VPS.

Introduction

I would like to share my idea of simplifying the process of cyclic updating free Let's Encypt certificates in a containerized environment. My favorite web hosting platform is Docker. Therefore, to implement and publish web applications I use Docker containers running on Linux VPS. In such an environment, I have many containers with web applications running behind one container with a nginx reverse proxy server. However, for the implementation of the HTTPS protocol for outdoor communication, I use free Let's Encypt certificates, which I manage using the Certbot tool. Although the described environment is undoubtedly a popular and great solution, it causes some problems.

Namely, without additional tools, I must remember to copy the certificate to the proxy server after renewal and then manually reload the website that uses the certificate. Although this is not a difficult task, it requires some attention, which could be devoted to more interesting activities. My idea of solving this small problem is quite simple and flexible. It allows me to completely automate the certificate update process and also allows me to avoid restarting the proxy server.

Background

The idea is to use the Certbot timer, which is responsible for automatic and cyclical renewal of certificates. Certbot installs on the system timer service called certbot.service, which automatically launches the process of renewing installed certificates from time to time.

For implementation, I wrote a few simple scripts that can be freely configured. These scripts install on the system two additional services that work with the Certbot timer. The first service I named certbot-renewed-copy.service is responsible for automatically copying renewed certificates to the proxy directory. The second service, called certbot-post-renewal-reload.service deals with reloading web application containers when certificates are renewed. The proxy server container is not reloaded, this only applies to application containers.

Wherever possible, Certbot installs certificates using the webroot method, because it does not require you to disable the proxy server using port 80.

I assumed that the web application containers are managed using the Docker Compose tool. In the configuration file of this tool, for a given container (docker-compose.yml), the domain names corresponding to the installed certificates should be specified in the environment: VIRTUAL_HOST parameter.

In addition, I assume that Certbot installs the certificates in the standard directory /etc/letsencrypt/live.

Launched services save their logs to a standard system journal. Therefore, they can be viewed in the status of a given service or using the journalctl tool.

I tested this solution on Debian 9 and Ubuntu 16.04 Linux distributions.

Using the code

Before starting the installation, copy all downloaded files into your directory of choice.

The installation procedure consists, in first, customizing the contents of configuration files and then running the script to install the services.

In the config.copy.cf file, you should edit the list of certificate domains that will be copied (certificates field) and the destination directory path where they will be copied for the proxy server (destination field).

For example:

certificates = domain.com, sub.domain.com
destination = /path/to/proxy/certs

In the config.reload.cf file, in the certs_path field, enter the same path to the proxy server directory as above where the certificates will be copied:

certs_path = /path/to/proxy/certs

The config.location.cf file contains a list of all locations of docker-compose.yml files which are intended for launching containers for applications that we intend to automatically reload after certificate renewal.

For example:

/path/to/docked/web/app1
/path/to/docked/api2

To install the scripts on the system and run the services described above, I prepared a simple script called install.sh.

Run it this way:

$ sudo bash install.sh

The status and logs of installed services can be checked using these commands:

$ sudo systemctl status certbot-renewed-copy.service
$ sudo systemctl status certbot-post-renewal-reload.service
This article was originally posted at https://github.com/atmdevnet/certbot-copy-reload

License

This article, along with any associated source code and files, is licensed under The MIT License

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About the Author

amatecki
Software Developer atmdev.net
Poland Poland
Professional software developer with 10+ years of experience in developing .net based web and desktop applications and... all this in order to solve Your problems.
Currently I'm working as a freelancer.
Look at https://atmdev.net for more info.

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