How to deploy a self-hosted Docker registry with self-signed certificates

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Illustration: Lisa Hornung/TechRepublic

When you need a Docker registry hosted on your LAN and you don’t want to go through the trouble of purchasing certificates from a Certificate Authority, what do you do? You deploy a registry using self-signed certificates.

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Although that process is a bit more complicated, it’s not so challenging that any IT admin can’t pull it off.

And I’m going to show you just how to do it.

What you’ll need

To make this work, you’ll need at least two machines, both of which have Docker installed. I’m going to demonstrate on Ubuntu Server 20.04 and Pop!_OS desktop. If you’re using a different operating system, you’ll need to alter the process accordingly.

How to create your directories

The first thing we’re going to do is create some directories to house the repository and the necessary certificates. I’m going to demonstrate this on my users’ home directory, but you can place them in any directory to which your user has access.

Create the base directory with:

mkdir ~/registry

Create the two subdirectories with:

mkdir ~/registry/certs

mkdir ~/registry/auth

Change in the certs directory with:

cd ~/registry/certs

Generate a private key with:

openssl genrsa 1024 > domain.key

Change the permissions for the new key with:

chmod 400 domain.key

Next, we need to generate our certificate. However, because of the way the authorization process now works, we must first create a san.cnf file with:

nano san.cnf

In that file, paste the following contents (making sure to edit accordingly):

[req]

default_bits  = 2048

distinguished_name = req_distinguished_name

req_extensions = req_ext

x509_extensions = v3_req

prompt = no

[req_distinguished_name]

countryName = XX

stateOrProvinceName = N/A

localityName = N/A

organizationName = Self-signed certificate

commonName = 120.0.0.1: Self-signed certificate

[req_ext]

subjectAltName = @alt_names

[v3_req]

subjectAltName = @alt_names

[alt_names]

IP.1 = 192.168.1.191

Make sure to change (at least) IP.1 = to match the IP address of your hosting server.

Save and close the file.

Generate the key with:

openssl req -new -x509 -nodes -sha1 -days 365 -key domain.key -out domain.crt -config san.cnf

Change into the auth directory with:

cd ../auth

We now must pull down the registry container and have it generate an htpasswd file. This is done with the command:

docker run --rm --entrypoint htpasswd registry:2.7.0 -Bbn USERNAME PASSWORD > htpasswd

Where USERNAME is a unique username and PASSWORD is a unique/strong password.

How to deploy the registry server

It’s now time to deploy the registry server. Change back to the base registry directory with:

cd ~/registry

Deploy the registry container with the command:

docker run -d \

--restart=always \

--name registry \

-v `pwd`/auth:/auth \

-v `pwd`/certs:/certs \

-v `pwd`/certs:/certs \

-e REGISTRY_AUTH=htpasswd \

-e REGISTRY_AUTH_HTPASSWD_REALM="Registry Realm" \

-e REGISTRY_AUTH_HTPASSWD_PATH=/auth/htpasswd \

-e REGISTRY_HTTP_ADDR=0.0.0.0:443 \

-e REGISTRY_HTTP_TLS_CERTIFICATE=/certs/domain.crt \

-e REGISTRY_HTTP_TLS_KEY=/certs/domain.key \

-p 443:443 \

registry:2.7.0

Your registry should now be running and accessible from the local machine. If, however, you want to access it from a remote system, we need to add a ca.crt file. You need to copy the contents of the ~/registry/certs/domain.crt file.

Log into your second machine and create a new directory with:

sudo mkdir -p /etc/docker/certs.d/SERVER:443

Where SERVER is the IP address of the machine hosting the registry.

Create the new file with:

sudo nano /etc/docker/certs.d/SERVER:443/ca.crt

Where SERVER is the IP address of the machine hosting the registry.

Paste the contents from the domain.crt file (from the hosting server) into this new file. Save and close the file.

How to login to the new registry

From the second machine, open a terminal window and log into your new Docker registry with the command:

docker login -u USER -p https://SERVER:443

Where USER is the user you added when you generated the htpasswd file above and SERVER is the IP address of the machine hosting the registry.

You should be prompted for a password. Upon successful authentication, you’ll see Login Succeeded.

Congratulations, you’re now able to use that self-hosted Docker registry for your container images.

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