What is a Container Registry? Explanation by Wallarm

What is a Container Registry?

By definition, a container registry is a centrally managed platform managing and storing container images. These images are cloud-deployed and can be further used as container workloads templates.

Developers, involved in developing container-based apps, can access this resource to push/pull the container-images.

Take note of the fact that it’s used widely in CI/CD and DevOps development approaches. Additionally, its penetration is deeper in Kubernetes and as an endpoint for container-based applications. In either usage scenario, a container registry aids greatly in image management and makes them accessible via a unified place.

Container Images  

An image comprises various entities and files crucial for application development. They are easy to scale and are often linked with CI/CD and DevOps development approaches. A system library to a system tool, all such components are their part.

Registries

As development goes on, numerous container-images are developed at different stages and their effective storage is important. Due to the ease of pulling into other systems provided by registries, most of the development experts prefer to keep images into them. 

They can be of 2 types: Public And Private. Each one acts in a different manner and will bring a different set of benefits. Hence, if you’ve plans to use registries, you must get familiar with both these varieties first.  

1. Public Registries

Let’s begin with public registries first as they are widely used. A container registry becomes a public register when it allows any user to store and share the container-image. Without any subscription, anyone can use these registries. Docker Hub is a very famous example in this regard.  

It features an official, copyrighted, and professional container-image that anyone can use. Mostly, these are open-source registries. But, few are freemium as well.  

2. Private Registries

It is a premise-dedicated registry that has a vendor-specific authority. Not always, it’s an on-premise resource. It could be cloud-hosted but is managed by a specific vendor who can decide the registry access, control the accessing, accept or reject the changes request. And owns the exclusive rights of the container images.

As a user of a private registry, you have no or very little hold over the images. You pay the subscription and use the image the way the admin or authority of the registry allows.

Now, each type comes with a certain set of pros and cons. For instance:

• You feel liberated with a public registry but you’re exposed to more threats as images are not audited or regulated
• Private registries will make you feel restricted but they keep tons of risks and hassles at bay. For instance, the vendor has to look into the security aspect of the registry. Security is more certain in this case.

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Decisive Scan Of The Container Registry

Whether you use a public registry like a Docker container registry or any private registry, certain risks are always around you. If the container images are not properly inspected before and after they become a part of a registry.

In fact, early scanning will lose its viability as security risks can also take place when an image becomes a part of a registry. Continual scanning, independent or with the help of 3rd party resources, showed up as a potential solution for this risk.

This is why many famous public and private container registries are now offered with an in-built scanning feature. Wondering why we’re focusing too much on container registry scanning? And why it’s important from an API security point of view? Try paying attention to the below-mentioned reasons.  

1. Protecting the development lifecycle

For fully automated DevOps and CI/CD development approaches, risks of unsecured registry configuration or uncontrolled access privilege are always high. The occurrence of these two threats paves the path for unverified and harmful container images.

Decisive scanning, at each development stage, is capable of identifying the potential harm-causing images. So that not a single unauthorized entity becomes a part of the registry. It even keeps an eye on the version history of the images and restricts non-permissible version updates.

2. Securing public images

As mentioned above, public registry images are free to use and are easy to exploit by a skilled set of hands. As there is no responsible entity to look into the public image security or the presence of malicious activities, their usage is always a risky affair.

You’re a little safe if you use official images from the public registry. However, such images could be an attack vendor without your knowledge.

The only viable solution to make public registry images safe for use is to integrate a vulnerability management tool. That will automatically assess the images for the presence of vulnerabilities by continual and periodic scanning.  

3. Avoiding disclosure of secrets

Container image secrets feature mission-critical data like passwords, access & private keys, passwords, and tokens. Such descriptive information is no less than a goldmine for the hackers. They can use them to successfully carry out an attack.  

With timed and scheduled scanning, it’s possible to protect registry secrets. It also ensures the timely implementation of corrective methods for every new image version.

4. Protection against malware and software supply chain risks

Knowingly or unknowingly, a container image can keep malware or corrupted script hidden.

These are the resources that hackers use to carry out an attack. The worst part here is that such kinds of attacks can exist during runtime and even bypass the customary signature-based and pattern-based scanners.

The ideal security solution here is to run images in a highly secured cloud hosted sandbox ecosystem. Such solutions are well-integrated into CI/CD pipeline and scan the concerned image in a fully functional state.

5. Detecting obsolete packages and libraries

As you already know, it’s not possible to make any changes to the container images once they are created. Changes are possible with the launch of the new version. This new version release process leaves many outdated packages and libraries left unattended.

Hackers can use these outdated entities to launch new vulnerabilities. Hence, their proper management is important. When you successfully integrate a scanner in CI/CD pipeline. By doing so, it’s effortless to spot the at-risk idle packages and get rid of them before they cause any nuisance.  

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How To Secure The Container Registry?

The container registry is here to ease down the development process. But, this doesn’t mean that developers must start using it blindly as certain security risks are tucked along with this. For instance, a hidden container image vulnerability has the potential to impact the stored containers & software apps where images are used.

Also, container images with poor security can become an attack vector in no time and can cause severe harm. Hence, its usage must be backed by sound and effective security solutions.  

Below-mentioned container registry security approaches are world-best and have proved their viability.

• Take the help of manifest and digest for referencing

Every container image comes with two unique elements; manifest and digest. Manifest, the JSON-based image description, features image specific details like tags and configuration instructions. Each image has a distinct manifest.

The SHA-256 manifest hash of an image is the digest. It’s responsible to allot every image a distinctive image referencing. By any chance, an image becomes a cyberpunk prey and faces any modification, the digest will bring it to the surface. With the help of these two, spotting unauthorized image modification is easy.

• Carry out periodic auditing

Any outdated resource, software, or container image, is a serious threat to the concerned systems and applications. With an outdated container image, you can’t expect immaculate container instances as such an image will only produce weak and negative outcomes.  

Another issue with dated container images is that they will allow persistence vulnerabilities to reach the application. The only resolution here is the container image update. Why go through so much trouble?

It’s better to conduct an audit before using a container image. In fact, schedule the audits at regular intervals so that no vulnerable image penetrates a container.

• Controlled user privileges

Over and uncontrolled container image usage is one of the key reasons behind the container-registry security issue. Hence, it’s a must to limit user privileges at a granular level. Practices like the least privilege principle and allowing access only for project-specific images are best for user privilege control.

Using these practices, certain limitations should be imposed. For instance, those who are using container images without any update writing must not be allowed to write access to that registry.

DevOps tools and other resources must enforce permission restrictions and programmed change request verification. No change request should be processed without going through extensive verification.

Registries with defined roles, a granular access ecosystem, and a strong verification process are always the best choice to make. Such an option will not entertain any access or registry contribution request that falls outside the permitted project’s scope.

In the case of 3rd party access, one has to be extra careful as such accesses, when not monitored properly, tend to pose more security risks to the CI/CD pipeline and container registry.

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What Should I Pay Attention To When Choosing a Container Registry?

Willing to make a wise choice while choosing a container registry? Be attentive and make sure you’re getting facilities like:

• Access control so that you can decide who can access the image why and for which reasons
• In-built security features like image scanner, audit controls, multiple logging, and so on
• Choosing the deployment type as per the need of the hour  
• Support for multiple data types to enjoy great flexibility

Keep these factors in mind and make a choice that suits the best with your requirements.

Choose The Best Container Registries

In case you’re willing to use this resource, you need to conduct extensive market research, access the offered options. Know them better, and pick one that aligns the best with your development goals. Here are some of the most promising options in the market.                                  

1. Azure Container Registry (ACR)

Offered by Microsoft, ACR is a feature-rich option with far-reaching capabilities. It’s a Docker Registry 2.0-based resource and is backed by the Azure RBAC authentication method.  

Some of its exceptional features include content trust, untagged manifests backed by retention policy, and purging for discarded or outdated images. These are exclusive features and are not offered by its peers.

Its content trust feature follows the Docker-based concept and permits developers to sign the pushed images. It also enables Docker clients to confirm the image integrity before using it. ACR does more than storing the container images. It enables developers to integrate OCI Artifacts, Helm Chart, and images in the development.  

2. Amazon ECR

With ECR, developers can use both the public and private Docker registries and can be easily paired with AWS IAM. As a supportive resource for AWS IAM, this option helps in controlling the access level of the users, applications, and related services.

The entire container image usage cycle, at the user level, can be monitored and controlled. Its in-built vulnerable image scanning capability makes it an ideal choice to make for the DevSecOps approach. What makes Amazon ECR stand out is its CVEs databases that help in figuring out the brutality of the existing security hazards.

Want to prevent image override? You have the facility of Immutable Image tags that AWS Elastic Container Registry (ECR) offers. No image overriding is possible when this feature is activated.

3. Docker Hub

It’s hard to beat the popularity of Docker Hub as this is the default option. Use it to access public container images for free. Yes, it won’t cost you a single penny to use the images it offers. This explains its huge popularity, especially among beginner-level developers.

However, this free availability is not always a boon as its usage in illegal mining of cryptocurrencies has been observed a couple of times. The image pull/push limitation worked a bit to control the ill usage of this container registry.

For seekers of professional features, it does offer a paid plan as well. Either way, it delivers great value.

4. GitLab Container Registry

Looking for a free container registry with Helm Chart capability? Try GitLab’s proprietary container image. Both its self-hosted and cloud-based versions are highly viable and proffer a clean-up policy. Using this policy, it’s easy to get rid of tags following the same regex arrangement.

With this option, you have the facility of Package Registry for free. If you’re an extensive GitLab for your projects, you must try this for sure.

5. GitHub Package Registry

After the huge success of the package registry, GitHub launched the container image in 2020. This is the best option to pick if you need seamless authentication as you enjoy end-to-end authentication using a personal access token.

Anyone willing to use it can complete the authentications directly from the GitHub credentials. Even though it’s not as feature-rich as Azure and AWS’s options, it’s still preferred by those using GitHub extensively without paying for imports.

Conclusion

Container images are an integral part of the CI/CD and DevOps pipeline and can automate the development up to a great extent. However, their effective usage depends on multiple factors like ensuring no over exploitation is happening, a scanner is in place to spot any threats, continual auditing is taking place. And you’ve got a registry that can suit the most as per your development goals.

Whether you use a public registry or private registry, you must enforce substantial security measures on container security.