ETCD

 

What is ETCD?

etcd is a distributed, consistent, highly-available key-value store used to store critical cluster data.

It is a core component of Kubernetes.

etcd port : 2379

 

Why ETCD Is Important

In Kubernetes, etcd stores the entire cluster state, including:

• Nodes

• Pods

• Services

• ConfigMaps

• Secrets

• Deployments

• RBAC policies

If etcd goes down → the cluster control plane stops functioning.

ETCD Architecture

etcd is based on:

• Distributed consensus algorithm: Raft

• Leader–Follower model

• Strong consistency

   

 High-Level Architecture

           ───────────────┐
          │   ETCD Leader │
          └───────┬───────┘
                  │
        ┌─────────┴─────────┐
        │                   │
┌───────────────┐   ┌───────────────┐
│     ETCD Follower │                      │ ETCD Follower │
└───────────────┘   └───────────────┘

 How Kubernetes Uses ETCD

 kubectl apply → API Server → etcd

•  User sends request
• API Server validates
• State stored in etcd
• Controllers reconcile state

 ETCD Data Storage

• Data stored as key-value pairs

• Hierarchical structure

Example keys in Kubernetes:

/registry/pods/default/nginx
/registry/services/default/my-service

ETCD Deployment in Kubernetes

Single Master (Not Recommended for Production)

 Master Node
 ├── kube-apiserver
 ├── kube-controller-manager
 ├── kube-scheduler
 └── etcd

  HA Multi-Master (Production)

Master 1 ─┐
Master 2 ─┼── etcd Cluster (3 or 5 nodes)
Master 3 ─┘

Best practice:

• 3 or 5 etcd members

• Odd number only (quorum)

Important ETCD Ports 

Port	Purpose
2379	Client communication
2380	Peer communication

ETCD Commands

Using etcdctl CLI:

Check Cluster Health

etcdctl endpoint health

List Members

etcdctl member list

Get Key

etcdctl get /registry/pods --prefix

Put Key

etcdctl put mykey "value"

Backup ETCD (Very Important in Production)

Take Snapshot

etcdctl snapshot save snapshot.db

 

Installing ETCD as a service 
 

✅ 1️⃣ Download etcd

Official binaries are available from the etcd GitHub releases.

Example (Linux):

 ETCD_VERSION=v3.5.12

wget https://github.com/etcd-io/etcd/releases/download/${ETCD_VERSION}/etcd-${ETCD_VERSION}-linux-amd64.tar.gz

tar -xvf etcd-${ETCD_VERSION}-linux-amd64.tar.gz
cd etcd-${ETCD_VERSION}-linux-amd64

sudo mv etcd etcdctl /usr/local/bin/

Verify:

etcd --version
etcdctl version

✅ 2️⃣ Create etcd User (Best Practice)

sudo useradd --system --no-create-home --shell /sbin/nologin etcd

Create data directory:

sudo mkdir -p /var/lib/etcd
sudo chown -R etcd:etcd /var/lib/etcd

✅ 3️⃣ Create systemd Service File

sudo nano /etc/systemd/system/etcd.service

 Paste  

[Unit]
Description=etcd key-value store
Documentation=https://etcd.io
After=network.target

[Service]
User=etcd
Type=notify
ExecStart=/usr/local/bin/etcd \
  --name node1 \
  --data-dir=/var/lib/etcd \
  --listen-client-urls=http://127.0.0.1:2379 \
  --advertise-client-urls=http://127.0.0.1:2379 \
  --listen-peer-urls=http://127.0.0.1:2380 \
  --initial-advertise-peer-urls=http://127.0.0.1:2380 \
  --initial-cluster=node1=http://127.0.0.1:2380 \
  --initial-cluster-state=new

Restart=always
RestartSec=5

[Install]
WantedBy=multi-user.target 

 ✅ 4️⃣ Start the Service

sudo systemctl daemon-reload
sudo systemctl enable etcd
sudo systemctl start etcd

 Check status:

sudo systemctl status etcd 

 ✅ 5️⃣ Test etcd

etcdctl put name "ckA-prep"
etcdctl get name

 If successful → etcd is running correctly 🎉

 

List all keys stored by Kubernetes :