Deploy A Private Docker Registry

Using Cloudflare for HTTPS

2 minutes read

As I previously mentioned in my post on deploying with docker-compose: I don’t want to push my docker images to public DockerHub repos. My images aren’t intended for public consumption and I don’t want to worry about keeping secrets out of my images.

I finally got around to deploying a private docker registry, and luckily, the Docker development team has made it so incredibly easy. Deployment is so simple, because the registry server itself is actually a docker container. Talk about self-hosted.

Digital Ocean has an excellent tutorial on deploying a docker registry, secured with HTTPS via Let’s Encrypt. I deploy most of my applications on Ubuntu droplets (which the tutorial targets), but the steps should easily translate to any major Linux distribution.

It’s nearly as simple as:

  1. Create /opt/docker-registry
  2. Create the data subdirectory
  3. docker-compose up -d on the provided docker-compose.yaml
  4. Reverse proxy the domain to the localhost port (nginx)
  5. Add a docker login account using htpasswd from apache2-utils

A Single Hiccup

The one issue I did have was using Cloudflare for HTTPS, instead of Let’s Encrypt/certbot.

After following the tutorial, I was able to log in just fine:

docker login https://my.registry.com

No problem.

But when I tried pushing my first image to the registry, I got a cryptic error:

$ docker push my.registry.com/my-image
The push refers to repository [my.registry.com/my-image]
91a6f9ebe82c: Pushing  3.584kB
8a90669ee51d: Retrying in 3 seconds 
37ea6c8b75fa: Pushing  3.584kB
14f687b6870a: Pushing  4.096kB
a638f39e4bbd: Pushing  3.072kB
4f8672401053: Waiting 
3e207b409db3: Waiting 
unknown blob

After doing some digging (googling) I found a stackoverflow answer (praise be!) that pinned the issue on the nginx proxy configuration.

I changed this line:

proxy_set_header  X-Forwarded-Proto $scheme;

To this:

proxy_set_header  X-Forwarded-Proto https;

Since I use the “Flexible” Cloudflare encryption, I suspect the request nginx recieves is actually an http request, which was causing the docker registry service to reject the request. By hard-coding the X-Forwarded-Proto as https, I circumvent the issue.

Is it a security concern? Perhaps, but I’ll accept that risk for now. Cloudflare is just so damn convenient.

UPDATE - July 27:

I managed to deploy SSL certificates to my nginx server – I didn’t realize Cloudflare let’s you generate (non-root) CA Certs for your domains, or I would have done this much sooner! I just uploaded the .pem files and updated the nginx config: now all traffic on port 80 is 301 Redirected to https. I’m now using Strict SSL for my Cloudflare domains.