This article points out the numerous benefits that you can achieve using an image pull policy in Kubernetes and how to properly choose an image pull policy and the factors that we should be wary of when choosing an image pull policy. You will find all the details here with proper explanation. You will also find the information on the benefits of using an image pull policy and what factors you should consider while choosing it. Let’s begin with the definition of Kubernetes image pull policy.
What Is the Kubernetes Image Pull Policy?
Kubernetes Image Policy is a mechanism in Kubernetes that allows you to restrict the images that can be pulled from a repository. The images can be pulled using the kubeadm image pull command or as part of a deployment manifest. The image pull policy can be configured for a specific namespace, a pod, or a set of pods using resource requests and limits.
Type of Modes
It has three modes:
- Allow any image to be pulled into the namespace.
- Allow only the images that match a specific criteria (e.g., tag) to be pulled into the namespace.
- Restrict all images from being pulled into the namespace.
The Image Policy object defines the list of allowed image tags and the list of forbidden tags. The Image Policy object is applied to a namespace. Then, it applies to all Pods that are created in it.
An image pull policy looks something like this:
containers:
- name: nginxdeployment
image: nginx:latestone
imagePullPolicy: IfNotPresent
ports:
- containerPort: 80
The term “imgePullPolicy:IfNotPresent” is displayed here. It currently has the value IfNotPresent. It indicates that if the container image is not already present on the host or worker that deploys the Kubernetes application, this option will pull it. In the case of the nginx:latest container image, for instance, Kubernetes won’t pull (download) it if the image already exists.
What Are the Benefits of Using an Image Pull Policy?
Using an image policy in your Kubernetes deployments has numerous advantages. The most obvious advantage is that it helps you make sure that your images are consistent and up to date.
However, there are many other benefits besides this if you implement an image policy. Here are some of the advantages of employing an image policy in your Kubernetes deployments:
The Images Are Current and Consistent
This allows you to update your application consistently whenever new features are added or when new vulnerabilities are discovered. This consistency enables you to simplify your deployment process and reduce the downtime for your users by ensuring that all of your applications always have the same features and the same base image.
It Helps You Simplify Your Deployment Process
An image pull policy is a set of best practices that help you simplify your deployment process by automating most of the tasks that you usually perform manually. For example, you can create an image pull policy that automatically installs all of the required dependencies for your application on fresh container without requiring you to type any of the commands yourself.
Increased Accuracy
Since image pull is a policy that specifies how the images are pulled from the remote storage by default, Kubernetes uses the latest image from the specified repository. However, using an image pull policy ensures that the image used is always the same as the one that is specified in the policy. This is especially important if you use an external registry to store your pictures since the images that are stored in that registry may differ from those that are stored in the Kubernetes cluster.
Which Factors to Consider When Choosing an Image Pull Policy
The many benefits of using the image pull policies make it worthwhile to go out of our way to implement them. But there are a lot of things to take into account when selecting an image pull policy for a Kubernetes deployment.
Here are some of the critical factors that you should consider:
The Frequency of Image Updates
How often do you need to update the images that you use in your containerized applications?
Your decision on how to manage your image repository should be based on the response to this question. If the application is long-lived, you may need to choose the git-lfs to retain a history of the image tags and content over time. For short-term applications, using Git may be a waste of resources because it requires you to keep a history of the blobs in your repository, increasing the storage size. If your application doesn’t require a record, it may be more cost-efficient to use something like a webhook to update a container’s image tag every time a new image is pushed to the repository. Using the Docker Hub Registry, you can use their Repository Image Pull Policy to manage how your pictures are updated based on your application requirements.
Image Format Support
What formats of images does your application use? Different applications may use other image formats depending on the type of containers that they are using. For example, you may run an Alpine Linux container that uses must by default, whereas a PHP application uses a CentOS-based image.
Policies Should Not Be Too Restrictive
One of the most critical factors that you should consider when choosing an image to pull policy is to make sure that the policies are not too restrictive and allow a continued innovation.
Policies Should Not Be Too Confusing
The policies should be written in a way that can be understood by developers, but also by the auditors and security professionals.
Having Balance in the Policies
It is vital to have a balance between these policies as they affect how easy it is for the developers to write the code and deploy it.
Conclusion
This article points out what Kubernetes’ image pull policy is. And due to the many benefits of using the image pull policies, we also discussed why we should go out of our way to use the image pull policies. This article further discusses the factors that you should consider before choosing an image pull policy to ensure that the image pull policies are best suited to your needs.
