Environment variables have a vital role in conventional systems, although not always significant. Some apps use environment variables more than others. Configuration files are preferred by some over environment variables.
However, environment variables are much more essential than you would expect for Kubernetes. It’s partly because of the way containers function in general and partly because of Kubernetes’ features. This blog will go through environment variables in Kubernetes and how to handle them.
So, what exactly are environmental variables, and why do they emerge?
Environment Variables Basics
Environment variables are traditionally dynamic key-value variables that are available to any process operating on the system. The operating system establishes many environment variables to assist running programs in understanding the system’s characteristics. As a result, software engineers may put logic in their applications that allows them to be tailored to a single operating system.
Environment variables also include a variety of critical information about the user, such as the user’s username, chosen language, user personal directory path, and a multitude of other useful bits of data.
In other words, Environment variables are a typical approach for developers to transfer application & infrastructure configuration out of application code and into an external source. One popular motivation for doing so is to make transitioning between environments easier. If you preserve the essential settings, you only need to relocate your app between development or testing machines; your program is more portable.
When a program executes on a computer, the variable becomes one of the process’s environments. These variables are usually set directly from a terminal, a configuration file in a home directory, or other tools.
Kubernetes and Environment Variables
In Kubernetes, the essential notion of environment variables is the same. Kubernetes, on the other hand, makes heavy use of environment variables for a variety of purposes. As a result, it’s important to comprehend the importance of environment variables in Kubernetes.
This is especially true if you’re migrating an existing application that doesn’t make extensive use of environment variables. Even if you don’t use any environment variables, you can still build pods. However, if you entirely disregard environment variables in Kubernetes, you may miss some of the more powerful Kubernetes capabilities.
Before we go any further, keep in mind that it’s typically a good idea to send the configuration to the Docker containers via environment variables wherever feasible when constructing microservices. This allows you to make the Docker image extra generic and potentially reusable for several applications. Let’s look at how you may inject certain environment variables into the Kubernetes pods with that in mind.
A Pod is a Kubernetes application’s fundamental execution unit that represents processes executing on the cluster.
When you build a Pod (using a Deployment, StatefulSet, or another method), you provide environment variables for the containers that run in it, which Kubernetes subsequently passes on to the application(s) inside it.
With Kubernetes, you may set environment variables directly in a configuration file, from an external configuration file, utilizing variables, or from a secrets file.
- The first choice is the easiest to understand. With the env keyword, you can easily provide environment variables in your deployment description.
- Passing environment variables from Kubernetes secrets is another approach to provide them to your application. As you might expect, this is a suitable choice for passing sensitive information such as passwords or tokens. As opposed to earlier, you don’t have to mention the value of the environment variable explicitly in the deployment. Instead, you tell Kubernetes to utilize the value of a secret object as the value of an environment variable for your Pod.
Using values from ConfigMaps is another technique to inject environment variables into the pods.
The primary difference between providing environment variables from ConfigMaps and defining them explicitly is that the life cycle of the environment variable is isolated from the life cycle of the Pod. This means you can change the value of your variable without having to wait for the Pod to finish executing.
To put it another way, you’ll have to manually restart the Pod for the updated values of the environment variables to be loaded into the Pod. When you include environment variables explicitly in the deployment, on the other hand, any change to the variables will instantly restart the Pod.
Read a Blog post: How Kubernetes has risen to be the operating system of the cloud?
Using Kubernetes Variables
Instead of setting a value directly using the value field, you may utilize ValueFrom to map environment variables to the values of Pod fields & container resources in your Kubernetes cluster.
From other fields
Field values are now limited to Pod metadata fields, name, service account name, as well as IP addresses, although this list may expand in the future.
The PRODUCT_BE_SERVER_URL environment variable is configured to the frontend application’s requirements using a label selector in the frontend deployment. Instead, you could use fieldRef to change the environment variable to the current IP address of the Pod executing the container.
The list of resource limitations and requests is now restricted to container CPU, memory, as well as storage limits & requests, but it may expand in the future.
While it works, the standard for the sample application backend deployment doesn’t include resource restrictions for containers, which is a terrible Kubernetes practice in general, especially when operating in production.
The code sample below from the backend deployment provides a MEMORY LIMIT environment variable to the container, which it and the apps executing in it may utilize by using resourceFieldRef.
Should “default” Configuration Values be Supplied?
Using the same default values for all the environment variables may appear to be a smart idea at first, but consider an application with hundreds of choices that must be specified before it can run.
It’s a lot of work to have your consumers fill in every single variable. Moreover, consumers may not be aware of all of the variables. Only until you need to edit a variable do you realize it exists. Otherwise, you might not know what value this parameter should be set to.
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