How to Use Registry with Podman on AlmaLinux

Podman has emerged as a strong alternative to Docker for managing containers, thanks to its secure and rootless architecture. When working with containerized environments, managing images efficiently is critical. A container image registry allows you to store, retrieve, and share container images seamlessly across environments. Whether you’re setting up a private registry for internal use or interacting with public registries, Podman provides all the necessary tools.

In this blog post, we’ll explore how to use a registry with Podman on AlmaLinux. This guide includes setup, configuration, and usage of both private and public registries to streamline your container workflows.

Introduction to Podman, AlmaLinux, and Container Registries

What is Podman?

Podman is an OCI-compliant container engine that allows users to create, run, and manage containers without requiring a daemon. Its rootless design makes it a secure option for containerized environments.

Why AlmaLinux?

AlmaLinux, a community-driven, RHEL-compatible distribution, is an excellent choice for hosting Podman. It offers stability, security, and enterprise-grade performance.

What is a Container Registry?

A container registry is a repository where container images are stored, organized, and distributed. Public registries like Docker Hub and Quay.io are widely used, but private registries provide more control, security, and customization.

Benefits of Using a Registry

Using a container registry with Podman offers several advantages:

1. Centralized Image Management: Organize and manage container images efficiently.
2. Version Control: Use tags to manage different versions of images.
3. Security: Private registries allow tighter control over who can access your images.
4. Scalability: Distribute images across multiple hosts and environments.
5. Collaboration: Share container images easily within teams or organizations.

Prerequisites

Before diving into the details, ensure the following:

1. AlmaLinux Installed: A running AlmaLinux system with sudo privileges.

2. Podman Installed: Install Podman using:

   sudo dnf install -y podman
   

3. Network Access: Ensure the system has network access to connect to registries or set up a private registry.

4. Basic Knowledge of Containers: Familiarity with container concepts and Podman commands.

Using Public Registries with Podman

Public registries like Docker Hub, Quay.io, and Red Hat Container Catalog are commonly used for storing and sharing container images.

Step 1: Search for an Image

To search for images on a public registry, use the podman search command:

podman search nginx

The output will list images matching the search term, along with details like name and description.

Step 2: Pull an Image

To pull an image from a public registry, use the podman pull command:

podman pull docker.io/library/nginx:latest

• docker.io/library/nginx: Specifies the image name from Docker Hub.
• :latest: Indicates the tag version. Default is latest if omitted.

Step 3: Run a Container

Run a container using the pulled image:

podman run -d --name webserver -p 8080:80 nginx

Access the containerized service by navigating to http://localhost:8080 in your browser.

Setting Up a Private Registry on AlmaLinux

Private registries are essential for secure and internal image management. Here’s how to set one up using docker-distribution.

Step 1: Install the Required Packages

Install the container image for a private registry:

sudo podman pull docker.io/library/registry:2

Step 2: Run the Registry

Run a private registry container:

podman run -d --name registry -p 5000:5000 -v /opt/registry:/var/lib/registry registry:2

• -p 5000:5000: Exposes the registry on port 5000.
• -v /opt/registry:/var/lib/registry: Persists registry data to the host.

Step 3: Verify the Registry

Check that the registry is running:

podman ps

Test the registry using curl:

curl http://localhost:5000/v2/

The response {} (empty JSON) confirms that the registry is operational.

Pushing Images to a Registry

Step 1: Tag the Image

Before pushing an image to a registry, tag it with the registry’s URL:

podman tag nginx:latest localhost:5000/my-nginx

Step 2: Push the Image

Push the image to the private registry:

podman push localhost:5000/my-nginx

Check the registry’s content:

curl http://localhost:5000/v2/_catalog

The output should list my-nginx.

Pulling Images from a Registry

Step 1: Pull an Image

To pull an image from the private registry:

podman pull localhost:5000/my-nginx

Step 2: Run a Container from the Pulled Image

Run a container from the pulled image:

podman run -d --name test-nginx -p 8081:80 localhost:5000/my-nginx

Visit http://localhost:8081 to verify that the container is running.

Securing Your Registry

Step 1: Enable Authentication

To add authentication to your registry, configure basic HTTP authentication.

1. Install httpd-tools:

   sudo dnf install -y httpd-tools
   

2. Create a password file:

   htpasswd -Bc /opt/registry/auth/htpasswd admin
   

Step 2: Secure with SSL

Use SSL to encrypt communications:

1. Generate an SSL certificate (or use a trusted CA certificate).
2. Configure Podman to use the certificate when accessing the registry.

Troubleshooting Common Issues

1. Image Push Fails

• Verify that the registry is running.
• Ensure the image is tagged with the correct registry URL.

2. Cannot Access Registry

• Check the firewall settings:

  sudo firewall-cmd --add-port=5000/tcp --permanent
  sudo firewall-cmd --reload
  

• Confirm the registry container is running.

3. Authentication Issues

• Ensure the htpasswd file is correctly configured.
• Restart the registry container after making changes.

Conclusion

Using a registry with Podman on AlmaLinux enhances your container workflow by providing centralized image storage and management. Whether leveraging public registries for community-maintained images or deploying a private registry for internal use, Podman offers the flexibility to handle various scenarios.

By following the steps in this guide, you can confidently interact with public registries, set up a private registry, and secure your containerized environments. Experiment with these tools to optimize your container infrastructure.

Let us know your thoughts or questions in the comments below. Happy containerizing!