| title | description | slug | weight |
|---|---|---|---|
HA Cluster |
Manage a Highly-Available Kubernetes Cluster |
HA Cluster |
4 |
Kubernetes utilizes a microservices architecture, with all requests initially directed to a central API server microservice, supported by various other components. For high availability in a Kubernetes cluster, it's common to add more control plane nodes, each hosting additional instances of the API Server, Scheduler, and Controller Manager. If etcd is part of the control plane nodes, additional members will also be added to the etcd cluster.
In a setup with multiple control plane nodes, several API Servers operate concurrently in a highly available configuration, all interfacing with the same etcd cluster. This setup ensures that client requests are processed consistently using the shared data. Communication with the API Servers is managed through a single endpoint, such as an external load balancer, which directs traffic to all API Server instances.
Other control plane components like the Scheduler and Controller Manager function on a failover basis. Among the instances of these microservices, one is elected as the active leader to handle all critical tasks. The other instances remain passive and only become active if the current leader fails.
High availability in the control plane is crucial but only part of achieving overall high availability in Kubernetes. For high availability of workloads, additional worker nodes might be necessary, and workloads should be configured to deploy multiple replicas that coordinate with each other.
Kubeadm simplifies the process of expanding your Kubernetes cluster by adding more nodes. To join a new node to the cluster, you first need to generate a join command that includes the API server's address, a unique join token, and the SHA hash of the cluster’s certificate authority (CA) certificate. This command can be generated using the following command on an existing control plane node:
sangam@sangam:~$
kubeadm token create --print-join-command
kubeadm join 192.168.129.135:6443 --token wahoal.dhn8p2qvkavuq7ge --discovery-token-ca-cert-hash sha256:d401c9e8831da53d4f85bb2b027b1a48f60408d0c241f105677c86e061ab2b4f
sangam@sangam:~$ sudo systemctl restart containerd
sangam@sangam:~$ sudo kubectl --kubeconfig /etc/kubernetes/admin.conf get nodes
NAME STATUS ROLES AGE VERSION
sangam Ready control-plane 47m v1.29.4
sangam@sangam:~$ sudo mkdir -p /etc/containerd
sudo containerd config default | sudo tee /etc/containerd/config.toml
disabled_plugins = []
imports = []
oom_score = 0
plugin_dir = ""
required_plugins = []
root = "/var/lib/containerd"
state = "/run/containerd"
temp = ""
version = 2
[cgroup]
path = ""
[debug]
address = ""
format = ""
gid = 0
level = ""
uid = 0
[grpc]
address = "/run/containerd/containerd.sock"
gid = 0
max_recv_message_size = 16777216
max_send_message_size = 16777216
tcp_address = ""
tcp_tls_ca = ""
tcp_tls_cert = ""
tcp_tls_key = ""
uid = 0
[metrics]
address = ""
grpc_histogram = false
[plugins]
[plugins."io.containerd.gc.v1.scheduler"]
deletion_threshold = 0
mutation_threshold = 100
pause_threshold = 0.02
schedule_delay = "0s"
startup_delay = "100ms"
[plugins."io.containerd.grpc.v1.cri"]
device_ownership_from_security_context = false
disable_apparmor = false
disable_cgroup = false
disable_hugetlb_controller = true
disable_proc_mount = false
disable_tcp_service = true
drain_exec_sync_io_timeout = "0s"
enable_selinux = false
enable_tls_streaming = false
enable_unprivileged_icmp = false
enable_unprivileged_ports = false
ignore_deprecation_warnings = []
ignore_image_defined_volumes = false
max_concurrent_downloads = 3
max_container_log_line_size = 16384
netns_mounts_under_state_dir = false
restrict_oom_score_adj = false
sandbox_image = "registry.k8s.io/pause:3.6"
selinux_category_range = 1024
stats_collect_period = 10
stream_idle_timeout = "4h0m0s"
stream_server_address = "127.0.0.1"
stream_server_port = "0"
systemd_cgroup = false
tolerate_missing_hugetlb_controller = true
unset_seccomp_profile = ""
[plugins."io.containerd.grpc.v1.cri".cni]
bin_dir = "/opt/cni/bin"
conf_dir = "/etc/cni/net.d"
conf_template = ""
ip_pref = ""
max_conf_num = 1
[plugins."io.containerd.grpc.v1.cri".containerd]
default_runtime_name = "runc"
disable_snapshot_annotations = true
discard_unpacked_layers = false
ignore_rdt_not_enabled_errors = false
no_pivot = false
snapshotter = "overlayfs"
[plugins."io.containerd.grpc.v1.cri".containerd.default_runtime]
base_runtime_spec = ""
cni_conf_dir = ""
cni_max_conf_num = 0
container_annotations = []
pod_annotations = []
privileged_without_host_devices = false
runtime_engine = ""
runtime_path = ""
runtime_root = ""
runtime_type = ""
[plugins."io.containerd.grpc.v1.cri".containerd.default_runtime.options]
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes]
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc]
base_runtime_spec = ""
cni_conf_dir = ""
cni_max_conf_num = 0
container_annotations = []
pod_annotations = []
privileged_without_host_devices = false
runtime_engine = ""
runtime_path = ""
runtime_root = ""
runtime_type = "io.containerd.runc.v2"
[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
BinaryName = ""
CriuImagePath = ""
CriuPath = ""
CriuWorkPath = ""
IoGid = 0
IoUid = 0
NoNewKeyring = false
NoPivotRoot = false
Root = ""
ShimCgroup = ""
SystemdCgroup = false
[plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime]
base_runtime_spec = ""
cni_conf_dir = ""
cni_max_conf_num = 0
container_annotations = []
pod_annotations = []
privileged_without_host_devices = false
runtime_engine = ""
runtime_path = ""
runtime_root = ""
runtime_type = ""
[plugins."io.containerd.grpc.v1.cri".containerd.untrusted_workload_runtime.options]
[plugins."io.containerd.grpc.v1.cri".image_decryption]
key_model = "node"
[plugins."io.containerd.grpc.v1.cri".registry]
config_path = ""
[plugins."io.containerd.grpc.v1.cri".registry.auths]
[plugins."io.containerd.grpc.v1.cri".registry.configs]
[plugins."io.containerd.grpc.v1.cri".registry.headers]
[plugins."io.containerd.grpc.v1.cri".registry.mirrors]
[plugins."io.containerd.grpc.v1.cri".x509_key_pair_streaming]
tls_cert_file = ""
tls_key_file = ""
[plugins."io.containerd.internal.v1.opt"]
path = "/opt/containerd"
[plugins."io.containerd.internal.v1.restart"]
interval = "10s"
[plugins."io.containerd.internal.v1.tracing"]
sampling_ratio = 1.0
service_name = "containerd"
[plugins."io.containerd.metadata.v1.bolt"]
content_sharing_policy = "shared"
[plugins."io.containerd.monitor.v1.cgroups"]
no_prometheus = false
[plugins."io.containerd.runtime.v1.linux"]
no_shim = false
runtime = "runc"
runtime_root = ""
shim = "containerd-shim"
shim_debug = false
[plugins."io.containerd.runtime.v2.task"]
platforms = ["linux/arm64/v8"]
sched_core = false
[plugins."io.containerd.service.v1.diff-service"]
default = ["walking"]
[plugins."io.containerd.service.v1.tasks-service"]
rdt_config_file = ""
[plugins."io.containerd.snapshotter.v1.aufs"]
root_path = ""
[plugins."io.containerd.snapshotter.v1.btrfs"]
root_path = ""
[plugins."io.containerd.snapshotter.v1.devmapper"]
async_remove = false
base_image_size = ""
discard_blocks = false
fs_options = ""
fs_type = ""
pool_name = ""
root_path = ""
[plugins."io.containerd.snapshotter.v1.native"]
root_path = ""
[plugins."io.containerd.snapshotter.v1.overlayfs"]
mount_options = []
root_path = ""
sync_remove = false
upperdir_label = false
[plugins."io.containerd.snapshotter.v1.zfs"]
root_path = ""
[plugins."io.containerd.tracing.processor.v1.otlp"]
endpoint = ""
insecure = false
protocol = ""
[proxy_plugins]
[stream_processors]
[stream_processors."io.containerd.ocicrypt.decoder.v1.tar"]
accepts = ["application/vnd.oci.image.layer.v1.tar+encrypted"]
args = ["--decryption-keys-path", "/etc/containerd/ocicrypt/keys"]
env = ["OCICRYPT_KEYPROVIDER_CONFIG=/etc/containerd/ocicrypt/ocicrypt_keyprovider.conf"]
path = "ctd-decoder"
returns = "application/vnd.oci.image.layer.v1.tar"
[stream_processors."io.containerd.ocicrypt.decoder.v1.tar.gzip"]
accepts = ["application/vnd.oci.image.layer.v1.tar+gzip+encrypted"]
args = ["--decryption-keys-path", "/etc/containerd/ocicrypt/keys"]
env = ["OCICRYPT_KEYPROVIDER_CONFIG=/etc/containerd/ocicrypt/ocicrypt_keyprovider.conf"]
path = "ctd-decoder"
returns = "application/vnd.oci.image.layer.v1.tar+gzip"
[timeouts]
"io.containerd.timeout.bolt.open" = "0s"
"io.containerd.timeout.shim.cleanup" = "5s"
"io.containerd.timeout.shim.load" = "5s"
"io.containerd.timeout.shim.shutdown" = "3s"
"io.containerd.timeout.task.state" = "2s"
[ttrpc]
address = ""
gid = 0
uid = 0
sangam@sangam:~$ sudo sed -i 's/ SystemdCgroup = false/ SystemdCgroup = true/' /etc/containerd/config.toml
sangam@sangam:~$ sudo systemctl restart containerd
k8s@k8s:~$ sudo kubeadm join 192.168.129.135:6443 --token wahoal.dhn8p2qvkavuq7ge --discovery-token-ca-cert-hash sha256:d401c9e8831da53d4f85bb2b027b1a48f60408d0c241f105677c86e061ab2b4f
[preflight] Running pre-flight checks
[preflight] Reading configuration from the cluster...
[preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Starting the kubelet
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap...
This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was received.
* The Kubelet was informed of the new secure connection details.
Run 'kubectl get nodes' on the control-plane to see this node join the cluster.
sangam@sangam:~$ sudo kubectl --kubeconfig /etc/kubernetes/admin.conf get nodes
NAME STATUS ROLES AGE VERSION
k8s Ready <none> 56s v1.29.4
sangam Ready control-plane 67m v1.29.4