Introduction
DaemonSets are a Kubernetes object that enables you to run a specific pod on each node in a cluster. Daemonsets are used for running daemon-like processes, such as log collectors, monitoring agents and other types of daemon-based services that need to be deployed on all nodes in a cluster.
In this blog post, we'll delve into the practical details of DaemonSets in Kubernetes, the concepts involved, how they work, and how to use them in your own deployment.
What is a DaemonSet in Kubernetes?
A DaemonSet is a Kubernetes object that creates a pod on each node in the cluster. DaemonSets enable you to run a specific pod on each node in the cluster, ensuring that all nodes have access to that pod.
DaemonSets are typically used for running processes that collect logs or metrics from the node, perform health checks, or monitor resource usage, as these types of processes need to be running on every node in the cluster.
By using DaemonSets, you can avoid having to manually deploy and manage these processes on every node in the cluster, thereby saving time and effort.
How do DaemonSets work in Kubernetes?
When you create a Daemonset in Kubernetes, Kubernetes creates a pod on each node in the cluster that matches the Daemonset's selectors. Once the pod is created, it continues to run on that node until the Daemonset is deleted or updated.
When you update a Daemonset, Kubernetes updates the pods on the nodes with the updated containers, ensuring that each node has the latest version of the desired pod running.
If a node is added or removed from the cluster, Kubernetes automatically creates or deletes the pods on that node to ensure that the desired number of Daemonset pods is running on each node in the cluster.
How to create a DaemonSet in Kubernetes?
Creating a Daemonset in Kubernetes is relatively straightforward. Here's an example YAML file that defines a Daemonset that creates an Nginx pod on each node in the cluster:
apiVersion: apps/v1
kind: DaemonSet
metadata:
name: nginx-daemonset
spec:
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:latest
ports:
- containerPort: 80
In the above YAML file, we first define the DaemonSet by specifying its kind and apiVersion. We then give it a name and specify the selectors that Kubernetes uses to identify the nodes on which to run the pods.
Next, we define the template for the pods that Kubernetes uses to create the pods. We give it a label so that Kubernetes only creates pods with that label. Finally, we specify the container details such as the name, image and ports.
Conclusion
DaemonSets are an essential Kubernetes object for running daemon-like processes that need to be deployed on every node in the cluster. DaemonSets are relatively easy to create and manage and can save a lot of time and effort.
In this blog post, we've covered what DaemonSets are, how they work, and how to create them in Kubernetes. By using DaemonSets in your own deployments, you can ensure that your daemon-based services are running on every node in the cluster, thereby ensuring maximum availability and reliability.