How can you tell what kind of Kubernetes Configmap you have?

A common point of confusion when working with Kubernetes is understanding how ConfigMap updates are handled. You’ve pushed a change to your ConfigMap, but your application isn't seeing the new values. What's going on?

The answer depends entirely on how your application consumes the ConfigMap. There isn't a "type" of ConfigMap object itself, but rather two distinct methods of consumption by a Pod, and each has drastically different behavior regarding updates.

To tell what "kind" you have, you need to look at your Pod or Deployment's YAML definition.

How to Check Your Pod's ConfigMap Consumption

You can find out how a Pod is using a ConfigMap by inspecting its YAML definition. 🧐 Run this command to get the running YAML for a specific pod:

Now, look for two key sections in the spec.containers list:

1. Environment Variables: Look for env or envFrom.
2. Mounted Volumes: Look for volumeMounts and the corresponding volumes section at the Pod spec level.

Let's break down what each one means for reloading.

1. Consumed as Environment Variables

This is when your Pod's YAML injects ConfigMap data directly as environment variables for the container.

How to Identify It

In your Pod spec, you'll see blocks like this:

If you see env or envFrom pointing to a configMapKeyRef or configMapRef, your application is consuming the ConfigMap as environment variables.

Reload Behavior: 🛑 No Hot-Reload

This is the most critical difference: Changes to a ConfigMap are NOT reflected in running Pods that use them as environment variables.

Environment variables are set by the container runtime only when the container is created. They are immutable for the life of that running process.

How to Apply Changes: To make the application see the new ConfigMap values, you must restart the Pod. The simplest way to do this for a Deployment is with a rolling restart:

When the new Pods are created, they will read the updated ConfigMap data and set the new environment variables.

2. Consumed as a Mounted Volume

This method mounts your ConfigMap as one or more files inside your Pod's filesystem. Your application is programmed to read its configuration from these files (e.g., /app/config/settings.properties).

How to Identify It

You'll see two corresponding sections in your Pod spec:

1. spec.containers.volumeMounts: This tells the container where to mount the volume.
2. spec.volumes: This defines the volume itself and links it to the ConfigMap.

If you see this volumes and volumeMounts pairing, your application is consuming the ConfigMap as files.

Reload Behavior: ✅ Automatic... With a Catch

This method does support hot-reloading, but with two important caveats:

1. There is a delay. When you update the ConfigMap object, the kubelet on the node is responsible for updating the mounted files. This is not instantaneous. It relies on a periodic sync cycle, and the total delay can be 60 to 90 seconds (or even longer) before the files at mountPath are actually updated.

2. Your application must support it. Kubernetes only updates the files on disk. It does not send a signal (like SIGHUP) to the process or restart the container. Your application must be built to:

   • Watch the configuration files for changes (using a library like fsnotify).
   • Periodically re-read the configuration files on its own timer.

If your application only reads its config files on startup, it will behave just like the environment variable method: it will not see the changes until it is restarted.

ConfigMap Reload Behavior Summary

Here’s a simple table to remember the differences:

| Consumption Method | How to Identify in Pod YAML | Are Changes Updated in Running Pod? | How Are Changes Seen? | | :--- | :--- | :--- | :--- | | Environment Variables | spec.containers.env spec.containers.envFrom | No ❌ | Pod must be restarted. | | Mounted Volume | spec.containers.volumeMounts spec.volumes | Yes ✅ (with delay) | Kubelet updates files. Application must be coded to reload the updated file. |

What If I Need Automatic Restarts?

If you are using the volume mount method but your application doesn't support live reloading, you can use a "reloader" tool. A popular open-source controller like Stakater's Reloader can watch for ConfigMap changes and automatically trigger a rolling restart of any Deployment that uses it. This gives you the best of both worlds: configuration in files and automatic updates for apps that can't reload on their own.

Skip the CLI. Power up with Kanvas

Alternatively, you can skip the YAML editing and make these changes visually. That is, if you're managing your Kubernetes cluster using Kanvas. Let's break down how to use it to manage your resources, like a ConfigMap.

🤔 What is Kanvas Designer?

Layer5's Kanvas is a powerful tool for designing, deploying, and managing your Kubernetes and Cloud infrastructure and workloads from a visual interface. Instead of writing hundreds of lines of YAML by hand, you build a Design. This design is a visual representation of your components (Deployment, Service, ConfigMap, etc.) and their relationships.

🎨 How to Update a ConfigMap in Kanvas Designer

Updating a ConfigMap through the Designer follows this "design-first" workflow. You don't just "edit" the live resource in the cluster; you update your design and then (re-)deploy it.

Here is the step-by-step process:

1. Open Kanvas Designer: Log in to your Kanvas UI and navigate to Designer mode (the default mode).

2. Load Your Design: Open the design file that contains the ConfigMap you want to edit. If you don't have a design yet, you can import your existing ConfigMap from your cluster directly onto the canvas.

3. Find the ConfigMap Component: On the visual canvas, find the block representing your ConfigMap. It will have the Kubernetes icon and the "ConfigMap" kind.

4. Edit the Configuration: Click on the component. A configuration panel will slide out, often with a 'Configure' tab or an editor icon. This will show you the key/value pairs for that specific ConfigMap resource.

5. Deploy the Design: Changes are automatically saved in your design as you make them. Use the Deploy button to send your entire design to your target Kubernetes or Cloud environment. Kanvas will calculate the difference (a "diff") and apply the updated ConfigMap manifest to your cluster. This action is the equivalent of running kubectl server-side apply using your design.

🛑 The Most Important Part: Reload Behavior

This is critical: Using Kanvas Designer to update a ConfigMap does NOT change how your application reloads it.

Deploying from Kanvas is just a friendly, visual way to run kubectl apply. The rules we discussed in our previous post about ConfigMap behavior still apply completely:

• If your Pod consumes the ConfigMap as Environment Variables: Your running Pods will not see the change. You must still restart them (e.g., kubectl rollout restart deployment ...).
• If your Pod consumes the ConfigMap as a Mounted Volume: The files inside the Pod will be updated (after the kubelet sync delay), but your application still needs to be smart enough to re-read that file from disk.

Kanvas Designer simplifies the applying of the change and helps you visually manage your application's state, but it doesn't change the fundamental Kubernetes behavior of how that change is consumed by your workloads.