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DaemonSets

Updated Apr 07, 2022 ·

Overview​

A DaemonSet is a Kubernetes resource similar to a Deployment, as it also creates Pods. However, its primary purpose is to ensure each node runs a copy of a specific Pod, commonly used for long-running processes.

  • When nodes are added, DaemonSets add Pods to them
  • When nodes are removed, the Pods are garbage collected.
  • Deleting a DaemonSet removes all its created Pods.

Some typical uses of a DaemonSet are:

  • Running a cluster storage daemon on every node
  • Running a logs collection daemon on every node
  • Running a node monitoring daemon on every node

Managing DaemonSets​

To check the DaemonSets running in the cluster, use:

kubectl get ds

For more detailed information about a DaemonSet in a specific namespace (e.g., kube-system), use:

kubectl describe <daemonset-name> -n kube-system

To see the daemonset in a specific namespace, e.g. kube-system:

kubectl get ds -n kube-system

Example output:

NAME        DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE
aws-node    2         2         2       2            2
kube-proxy  2         2         2       2            2

In the example above, there are two DaemonSets running:

  • kube-proxy

    • Handles iptables configs of the nodes
    • Allows network connectivity to happen with the pods on the node.
    kubectl logs -n kube-system kube-proxy-XXXXX

  • aws-node

    • Handles network overlay underneath
    • Contains the CNI plugins enabling EC2 nodes to talk to Amazon VPC CNI.
    kubectl describe ds aws-node -n kube-system

Default DaemonSets​

When a Kubernetes cluster is created, certain default DaemonSets, like the kube-proxy DaemonSet, are included for core networking functions.

To examine the logs of one of the kube-proxy Pods, list them first:

kubectl get pods -n kube-system | grep proxy

Example output:

kube-proxy-f8dl7                                                   1/1     Running   3 (6m58s ago)   140d
kube-proxy-fdmnb                                                   1/1     Running   0               5m23s
kube-proxy-nhzsd                                                   1/1     Running   0               5m17s

To retrieve logs from the first kube-proxy Pod, run:

# proxy_pod_1 is a variable with the name of the first kube-proxy pod
proxy_pod_1=$(kubectl get pods -n kube-system | grep proxy | cut -d" " -f1 | head -1)

kubectl logs -n kube-system $proxy_pod_1

This log shows network setup details and Pod-specific configurations, including IP address detection, proxy modes, and system settings adjustments.

I1228 15:55:44.614375       1 node.go:163] Successfully retrieved node IP: 10.0.0.100
I1228 15:55:44.614936       1 server_others.go:138] "Detected node IP" address="10.0.0.100"
I1228 15:55:44.615089       1 server_others.go:578] "Unknown proxy mode, assuming iptables proxy" proxyMode=""
I1228 15:55:44.842402       1 server_others.go:206] "Using iptables Proxier"
I1228 15:55:44.842586       1 server_others.go:213] "kube-proxy running in dual-stack mode" ipFamily=IPv4
I1228 15:55:44.842673       1 server_others.go:214] "Creating dualStackProxier for iptables"
I1228 15:55:44.842814       1 server_others.go:501] "Detect-local-mode set to ClusterCIDR, but no IPv6 cluster CIDR defined, , defaulting to no-op detect-local for IPv6"
I1228 15:55:44.842884       1 proxier.go:259] "Setting route_localnet=1, use nodePortAddresses to filter loopback addresses for NodePorts to skip it https://issues.k8s.io/90259"
I1228 15:55:44.843065       1 proxier.go:259] "Setting route_localnet=1, use nodePortAddresses to filter loopback addresses for NodePorts to skip it https://issues.k8s.io/90259"
I1228 15:55:44.843261       1 server.go:661] "Version info" version="v1.24.3"
I1228 15:55:44.843277       1 server.go:663] "Golang settings" GOGC="" GOMAXPROCS="" GOTRACEBACK=""
I1228 15:55:44.844361       1 conntrack.go:100] "Set sysctl" entry="net/netfilter/nf_conntrack_max" value=131072
I1228 15:55:44.844397       1 conntrack.go:52] "Setting nf_conntrack_max" nf_conntrack_max=131072
I1228 15:55:44.844659       1 conntrack.go:83] "Setting conntrack hashsize" conntrack hashsize=32768
I1228 15:55:44.858856       1 conntrack.go:100] "Set sysctl" entry="net/netfilter/nf_conntrack_tcp_timeout_close_wait" value=3600
I1228 15:55:44.861250       1 config.go:317] "Starting service config controller"
I1228 15:55:44.862031       1 shared_informer.go:255] Waiting for caches to sync for service config
I1228 15:55:44.862067       1 config.go:444] "Starting node config controller"
I1228 15:55:44.862072       1 shared_informer.go:255] Waiting for caches to sync for node config
I1228 15:55:44.864557       1 config.go:226] "Starting endpoint slice config controller"
I1228 15:55:44.864567       1 shared_informer.go:255] Waiting for caches to sync for endpoint slice config
I1228 15:55:44.962638       1 shared_informer.go:262] Caches are synced for service config
I1228 15:55:44.962638       1 shared_informer.go:262] Caches are synced for node config
I1228 15:55:44.964885       1 shared_informer.go:262] Caches are synced for endpoint slice config

To retrieve the YAML configuration of a running DaemonSet:

kubectl get daemonset $proxy_pod_1 -n kube-system -o yaml

Example output:

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: monitoring-daemon 
spec:
  selector:
    matchLabels:
      app: monitoring-agent
  template:
    metadata:
      labels:
        app: monitoring-agent
    spec:
      containers:
      - name: monitoring-agent
        image: monitoring-agent

For more information, please see DaemonSets in Kubernetes.