What are Daemon Set?

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 What are DaemonSets?

 

DaemonSets are a type of Kubernetes controller that is used to manage a set of pods on each node in a Kubernetes cluster. A DaemonSet ensures that all (or some) nodes in a cluster run a copy of a pod. As nodes are added to or removed from a cluster, the DaemonSet automatically adds or removes pods to ensure that the specified number of pods is running on each node. In other words, a DaemonSet makes sure that a copy of a pod is running on every node in a Kubernetes cluster.

 

DaemonSets are particularly useful for running system-level services or applications that need to be run on every node in a cluster, such as a logging agent or a monitoring tool. These services or applications can be critical for the overall health and stability of the cluster, and DaemonSets ensure that they are always available.

 

Examples of DaemonSets in Kubernetes

 

Let's take a look at some examples of how DaemonSets can be used in Kubernetes.

 

Example 1: Running a Logging Agent

 

One common use case for DaemonSets is running a logging agent on each node in a cluster. A logging agent collects log files from each node and sends them to a centralized logging service. Here's an example DaemonSet manifest for running a logging agent:

 

apiVersion: apps/v1

kind: DaemonSet

metadata:

  name: logging-agent

spec:

  selector:

    matchLabels:

      app: logging-agent

  template:

    metadata:

      labels:

        app: logging-agent

    spec:

      containers:

      - name: logging-agent

        image: logging-agent:latest

        volumeMounts:

        - name: var-log

          mountPath: /var/log

      volumes:

      - name: var-log

        hostPath:

          path: /var/log

 

 

In this example, we create a DaemonSet named "logging-agent" that runs a single container named "logging-agent" on each node. The container is based on the image "logging-agent:latest" and mounts the host's "/var/log" directory as a volume. This ensures that the logging agent can collect log files from each node.

 

Example 2: Running a Monitoring Tool

 

Another common use case for DaemonSets is running a monitoring tool on each node in a cluster. A monitoring tool collects metrics and other system-level information from each node and sends it to a centralized monitoring service. Here's an example DaemonSet manifest for running a monitoring tool:

apiVersion: apps/v1

kind: DaemonSet

metadata:

  name: monitoring-agent

spec:

  selector:

    matchLabels:

      app: monitoring-agent

  template:

    metadata:

      labels:

        app: monitoring-agent

    spec:

      containers:

      - name: monitoring-agent

        image: monitoring-agent:latest

        volumeMounts:

        - name: proc

          mountPath: /host/proc

        - name: sys

          mountPath: /host/sys

        - name: var-run-docker-sock

          mountPath: /var/run/docker.sock

      volumes:

      - name: proc

        hostPath:

          path: /proc

      - name: sys

        hostPath:

          path: /sys

      - name: var-run-docker-sock

        hostPath:

          path: /var/run/docker.sock

 

 

In this example

we create a DaemonSet named "monitoring-agent" that runs a single container named "monitoring-agent" on each node. The container is based on the image "monitoring-agent:latest" and mounts several host paths as volumes, including "/proc", "/sys", and "/var/run/docker.sock". This ensures that the monitoring tool can collect metrics and other system-level information from each node.

 

Example 3: Running a Proxy Server

 

DaemonSets can also be used to run proxy servers on each node in a cluster. A proxy server acts as an intermediary between clients and servers, and can be used to distribute traffic across multiple nodes. Here's an example DaemonSet manifest for running a proxy server:

 

apiVersion: apps/v1

kind: DaemonSet

metadata:

  name: proxy-server

spec:

  selector:

    matchLabels:

      app: proxy-server

  template:

    metadata:

      labels:

        app: proxy-server

    spec:

      containers:

      - name: proxy-server

        image: proxy-server:latest

        ports:

        - containerPort: 80

          hostPort: 80

        - containerPort: 443

          hostPort: 443

 

 

In this example, we create a DaemonSet named "proxy-server" that runs a single container named "proxy-server" on each node. The container is based on the image "proxy-server:latest" and exposes ports 80 and 443. By using hostPort, the container's ports are mapped directly to the host's ports, allowing the proxy server to receive traffic directly from clients.

 

Conclusion

 

DaemonSets are a powerful Kubernetes controller that can be used to ensure that a specific set of pods is running on each node in a cluster. They are particularly useful for running system-level services or applications that need to be run on every node in a cluster, such as logging agents, monitoring tools, and proxy servers. By using DaemonSets, you can ensure that these critical services or applications are always available, no matter how large or complex your Kubernetes cluster becomes

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