# Update ConfigMap without restarting Pods in Kubernetes
*This blog is basically a tip around Kubernetes Administration.*
I am assuming you know about and have some experience in Kubernetes & ConfigMaps.
Anyways I will try to explain concepts as easy as possible 😀
---
This is how I used to feel when I started :
So Don't worry, Let's start improving ourselves, no matter how much but consistently 👍
---
### When We use ConfigMaps?
When you want to supply environment-specific config values like env vars.
Using ConfigMaps, You can also mount your config as files in a particular directory which can be later read by our application.
So, In Short, using ConfigMaps, you can supply configs by :
1. Setting up env vars
2. Mounting the config values as a file (aka data volume).
### Problem Statement
**You updated a ConfigMap, Now you want to propagate this updated change to all existing running Pods.**
### Options
#### Option #1
**You can delete existing pods or restart the deployment rollout.**
But You know what this is not feasible in some cases where you don't want any downtime or you simply just don't want to delete any running Pods.
**Note** - if you are using ConfigMaps to set **env vars** then **this is the only option you have.**
#### Option #2
This option is only applicable if you have mounted your ConfigMap as a file in your Pod. Also if you are using ConfigMap as a [subPath](https://kubernetes.io/docs/concepts/storage/volumes/#using-subpath) volume, this option won't be applicable.
So Let's discuss this option in detail.
### The Option #2
This is not something which I have invented, rather I read this on the Official K8s docs page [here](https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/#mounted-configmaps-are-updated-automatically)
Actually, there are two ways you can achieve this,
#### 1. Use Annotation
According to the docs I mentioned above, You can update the pod's annotations which will trigger a refresh and your ConfigMap data volume will be populated with the latest data. Simple! 👀
#### 2. Wait for Kubelet to refresh ConfigMap data
If configured, Kubelet also tries to refresh the ConfigMaps for pods periodically to keep things in sync. This interval is called **ConfigMap Cache TTL**
**Extra** - There is one property called **ConfigMapAndSecretChangeDetectionStrategy** which you can configure when you start Kubelet. Possible values we can pass to this are : **Get**, **Cache** & **Watch** (Default)
This property defines how we want Kubelet to detect and propagate ConfigMap and Secret changes.
More info : [ConfigMaps | Kubernetes](https://kubernetes.io/docs/concepts/configuration/configmap/#mounted-configmaps-are-updated-automatically).
---
I hope this quick & short blog made sense :)
---
### Terminology Used
**Kubernetes** - Kubernetes is an open-source container orchestration system for automating software deployment, scaling, and management.
**Containers** - A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.
**Pods** - Pods are the smallest, most basic deployable objects in Kubernetes. Pods contain one or more containers.
**ConfigMaps** - A ConfigMap allows you to decouple environment-specific configuration (mostly environment variables) from your container images so that your applications are easily portable.
---
### References
1. https://en.wikipedia.org/wiki/Kubernetes
2. https://www.docker.com/resources/what-container
3. https://kubernetes.io/docs/concepts/configuration/configmap/
4. https://kind.sigs.k8s.io/docs/user/quick-start/
5. https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/#mounted-configmaps-are-updated-automatically
6. https://kubernetes.io/docs/concepts/configuration/configmap/#mounted-configmaps-are-updated-automatically