How To Set Up a Private Docker Registry on Ubuntu

Step 1 — Installing and Configuring the Docker Registry

Docker on the command line is useful when starting out and testing containers, but proves to be unwieldy for bigger deployments involving multiple containers running in parallel.

With Docker Compose, you can write one .yml file to set up each container’s configuration and information the containers need to communicate with each other. You can use the docker-compose command-line tool to issue commands to all the components that make up your application, and control them as a group.

Docker Registry is itself an application with multiple components, so you will use Docker Compose to manage it. To start an instance of the registry, you’ll set up a docker-compose.yml file to define it and the location on disk where your registry will be storing its data.

You’ll store the configuration in a directory called docker-registry on the main server. Create it by running:

Navigate to it:

Then, create a subdirectory called data, where your registry will store its images:

Create and open a file called docker-compose.yml by running:

Add the following lines, which define a basic instance of a Docker Registry:

version: '3'

services:
  registry:
    image: registry:2
    ports:
    - "5000:5000"
    environment:
      REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY: /data
    volumes:
      - ./data:/data

First, you name the first service registry, and set its image to registry, version 2. Then, under ports, you map the port 5000 on the host to the port 5000 of the container. This allows you to send a request to port 5000 on the server, and have the request forwarded to the registry.

In the environment section, you set the REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY variable to /data, specifying in which volume it should store its data. Then, in the volumes section, you map the /data directory on the host file system to /data in the container, which acts as a passthrough. The data will actually be stored on the host’s file system.

Save and close the file.

You can now start the configuration by running:

The registry container and its dependencies will be downloaded and started.

You’ll address the No HTTP secret provided warning message later in this tutorial. Notice that the last line of the output shows it has successfully started listening on port 5000.

You can press CTRL+C to stop its execution.

In this step, you have created a Docker Compose configuration that starts a Docker Registry listening on port 5000. In the next steps, you’ll expose it at your domain and set up authentication.

Step 2 — Setting Up Nginx Port Forwarding

As part of the prerequisites, you’ve enabled HTTPS at your domain. To expose your secured Docker Registry there, you’ll only need to configure Nginx to forward traffic from your domain to the registry container.

You have already set up the /etc/nginx/sites-available/your_domain file, containing your server configuration. Open it for editing by running:

Find the existing location block:

...
location / {
  ...
}
...

You need to forward traffic to port 5000, where your registry will be listening for traffic. You also want to append headers to the request forwarded to the registry, which provides additional information from the server about the request itself. Replace the existing contents of the location block with the following lines:

...
location / {
    # Do not allow connections from docker 1.5 and earlier
    # docker pre-1.6.0 did not properly set the user agent on ping, catch "Go *" user agents
    if ($http_user_agent ~ "^(docker\/1\.(3|4|5(?!\.[0-9]-dev))|Go ).*$" ) {
      return 404;
    }

    proxy_pass                          http://localhost:5000;
    proxy_set_header  Host              $http_host;   # required for docker client's sake
    proxy_set_header  X-Real-IP         $remote_addr; # pass on real client's IP
    proxy_set_header  X-Forwarded-For   $proxy_add_x_forwarded_for;
    proxy_set_header  X-Forwarded-Proto $scheme;
    proxy_read_timeout                  900;
}
...

The if block checks the user agent of the request and verifies that the version of the Docker client is above 1.5, as well as that it’s not a Go application that’s trying to access. For more explanation on this, you can find the nginx header configuration in Docker’s registry Nginx guide.

Save and close the file when you’re done. Apply the changes by restarting Nginx:

If you get an error, double-check the configuration you’ve added.

To confirm that Nginx is properly forwarding traffic to your registry container on port 5000, run it:

Then, in a browser window, navigate to your domain and access the v2 endpoint, like so:

https://your_domain/v2

You will see an empty JSON object:

{}

In your terminal, you’ll receive output similar to the following:

registry_1  | time="2018-11-07T17:57:42Z" level=info msg="response completed" go.version=go1.7.6 http.request.host=cornellappdev.com http.request.id=a8f5984e-15e3-4946-9c40-d71f8557652f http.request.method=GET http.request.remoteaddr=128.84.125.58 http.request.uri="/v2/" http.request.useragent="Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_2) AppleWebKit/604.4.7 (KHTML, like Gecko) Version/11.0.2 Safari/604.4.7" http.response.contenttype="application/json; charset=utf-8" http.response.duration=2.125995ms http.response.status=200 http.response.written=2 instance.id=3093e5ab-5715-42bc-808e-73f310848860 version=v2.6.2
registry_1  | 172.18.0.1 - - [07/Nov/2018:17:57:42 +0000] "GET /v2/ HTTP/1.0" 200 2 "" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_2) AppleWebKit/604.4.7 (KHTML, like Gecko) Version/11.0.2 Safari/604.4.7"

You can see from the last line that a GET request was made to /v2/, which is the endpoint you sent a request to, from your browser. The container received the request you made, from the port forwarding, and returned a response of {}. The code 200 in the last line of the output means that the container handled the request successfully.

Press CTRL+C to stop its execution.

Now that you have set up port forwarding, you’ll move on to improving the security of your registry.

Step 3 — Setting Up Authentication

Nginx allows you to set up HTTP authentication for the sites it manages, which you can use to limit access to your Docker Registry. To achieve this, you’ll create an authentication file with htpasswd and add username and password combinations to it that will be accepted.

You can obtain the htpasswd utility by installing the apache2-utils package. Do so by running:

You’ll store the authentication file with credentials under ~/docker-registry/auth. Create it by running:

Navigate to it:

Create the first user, replacing username with the username you want to use. The -B flag orders the use of the bcrypt algorithm, which Docker requires:

Enter the password when prompted, and the combination of credentials will be appended to registry.password.

Note: To add more users, re-run the previous command without -c, which creates a new file:

Now that the list of credentials is made, you’ll edit docker-compose.yml to order Docker to use the file you created to authenticate users. Open it for editing by running:

Add the highlighted lines:

version: '3'

services:
  registry:
    image: registry:2
    ports:
    - "5000:5000"
    environment:
      REGISTRY_AUTH: htpasswd
      REGISTRY_AUTH_HTPASSWD_REALM: Registry
      REGISTRY_AUTH_HTPASSWD_PATH: /auth/registry.password
      REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY: /data
    volumes:
      - ./auth:/auth
      - ./data:/data

You’ve added environment variables specifying the use of HTTP authentication and provided the path to the file htpasswd created. For REGISTRY_AUTH, you have specified htpasswd as its value, which is the authentication scheme you are using, and set REGISTRY_AUTH_HTPASSWD_PATH to the path of the authentication file. REGISTRY_AUTH_HTPASSWD_REALM signifies the name of htpasswd realm.

You’ve also mounted the ./auth directory to make the file available inside the registry container. Save and close the file.

You can now verify that your authentication works correctly. First, navigate to the main directory:

Then, run the registry by executing:

In your browser, refresh the page of your domain. You’ll be asked for a username and password.

After providing a valid combination of credentials, you’ll see an empty JSON object:

{}

This means that you’ve successfully authenticated and gained access to the registry. Exit by pressing CTRL+C.

Your registry is now secured and can be accessed only after authentication. You’ll now configure it to run as a background process while being resilient to reboots by starting automatically.

Step 4 — Starting Docker Registry as a Service

You can ensure that the registry container starts every time the system boots up, or after it crashes, by instructing Docker Compose to always keep it running. Open docker-compose.yml for editing:

Add the following line under the registry block:

...
  registry:
    restart: always
...

Setting restart to always ensures that the container will survive reboots. When you’re done, save and close the file.

You can now start your registry as a background process by passing in -d:

With your registry running in the background, you can freely close the SSH session, and the registry won’t be affected.

Because Docker images may be very large in size, you’ll now increase the maximum file size that Nginx will accept for uploads.

Step 5 — Increasing File Upload Size for Nginx

Before you can push an image to the registry, you need to ensure that your registry will be able to handle large file uploads.

The default size limit of file uploads in Nginx is 1m, which is not nearly enough for Docker images. To raise it, you’ll modify the main Nginx config file, located at /etc/nginx/nginx.conf. Open it for editing by running:

Find the http section, and add the following line:

...
http {
        client_max_body_size 16384m;
        ...
}
...

The client_max_body_size parameter is now set to 16384m, making the maximum upload size equal to 16GB.

Save and close the file when you’re done.

Restart Nginx to apply the configuration changes:

You can now upload large images to your Docker Registry without Nginx blocking the transfer or erroring out.

Step 6 — Publishing to Your Private Docker Registry

Now that your Docker Registry server is up and running, and accepting large file sizes, you can try pushing an image to it. Since you don’t have any images readily available, you’ll use the ubuntu image from Docker Hub, a public Docker Registry, to test.

From your second, client server, run the following command to download the ubuntu image, run it, and get access to its shell:

The -i and -t flags give you interactive shell access into the container.

Once you’re in, create a file called SUCCESS by running:

By creating this file, you have customized your container. You’ll later use it to check that you’re using exactly the same container.

Exit the container shell by running:

Now, create a new image from the container you’ve just customized:

The new image is now available locally, and you’ll push it to your new container registry. First, you have to log in:

When prompted, enter in a username and password combination that you’ve defined in step 3 of this tutorial.

The output will be:

...
Login Succeeded

Once you’re logged in, rename the created image:

Finally, push the newly tagged image to your registry:

You’ll receive output similar to the following:

The push refers to a repository [your_domain/test-image]
420fa2a9b12e: Pushed
c20d459170d8: Pushed
db978cae6a05: Pushed
aeb3f02e9374: Pushed
latest: digest: sha256:88e782b3a2844a8d9f0819dc33f825dde45846b1c5f9eb4870016f2944fe6717 size: 1150

You’ve verified that your registry handles user authentication by logging in, and allows authenticated users to push images to the registry. You’ll now try pulling the image from your registry.

Step 7 — Pulling From Your Private Docker Registry

Now that you’ve pushed an image to your private registry, you’ll try pulling from it.

On the main server, log in with the username and password you set up previously:

Try pulling the test-image by running:

Docker should download the image. Run the container with the following command:

List the files present by running:

You will see the SUCCESS file you’ve created earlier, confirming that its the same image you’ve created:

SUCCESS  bin  boot  dev  etc  home  lib  lib64  media   mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

Exit the container shell by running:

Now that you’ve tested pushing and pulling images, you’ve finished setting up a secure registry that you can use to store custom images.