Cluster upgrade strategies in Kubernetes - Step-by-Step Execution

Process Flow - Cluster upgrade strategies

Start: Current Cluster Version

↓

Choose Upgrade Strategy

↓

In-place

↓

Upgrade Nodes

↓

Verify & Test

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Complete Upgrade & Cleanup

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End

This flow shows the main steps in upgrading a Kubernetes cluster using different strategies: in-place, blue-green, and canary/rolling upgrades.

Execution Sample

Kubernetes

kubectl drain node1 --ignore-daemonsets
# Upgrade node (e.g., kubeadm upgrade node on node1)
kubectl uncordon node1

This sequence drains a node, upgrades it, then brings it back to the cluster.

Process Table

Step	Action	Node State	Cluster State	Result
1	Drain node1	cordoned, pods evicted	Ready nodes reduced by 1	Node1 ready for upgrade
2	Upgrade node1	upgrading	Cluster running with node1 offline	Node1 updated to new version
3	Uncordon node1	ready	All nodes ready, cluster upgraded	Node1 back in service
4	Verify cluster	all nodes ready	Cluster version updated	Upgrade successful
5	Exit	N/A	N/A	Upgrade complete, cluster stable

💡 All nodes upgraded and cluster is stable with new version

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
node1_state	ready	cordoned	upgrading	ready	ready
cluster_ready_nodes	3	2	2	3	3
cluster_version	v1.20	v1.20	v1.20	v1.21	v1.21

Key Moments - 3 Insights

Why do we drain the node before upgrading?

Draining the node safely evicts pods so workloads move to other nodes, preventing downtime during upgrade (see execution_table step 1).

What happens if we uncordon the node before upgrade finishes?

The node might be unstable or incompatible, causing errors. The upgrade must complete before uncordoning (see execution_table step 3).

How does cluster version change during upgrade?

Cluster version updates only after node upgrade completes and node rejoins ready state (see variable_tracker cluster_version changes at step 3 and 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the node1 state after step 2?

A upgrading

B ready

C cordoned

D drained

💡 Hint

Check the 'Node State' column for step 2 in the execution_table.

At which step does the cluster version update?

A Step 1

B Step 2

C Step 4

D Step 3

💡 Hint

Look at the 'cluster_version' variable in variable_tracker after each step.

If we skip draining the node, what likely happens?

A Node upgrades faster

B Pods remain running on node during upgrade, causing downtime

C Cluster version updates automatically

D Node is automatically uncordoned

💡 Hint

Refer to key_moments about why draining is important before upgrade.

Concept Snapshot

Cluster Upgrade Strategies:
- In-place: drain node, upgrade, uncordon
- Blue-Green: create new cluster, switch traffic
- Canary/Rolling: upgrade subset, monitor, rollback if needed
Always drain nodes before upgrade to avoid downtime.
Verify cluster stability after upgrade.

Full Transcript

This visual execution shows how Kubernetes cluster upgrades happen step-by-step. First, you drain a node to safely move workloads away. Then you upgrade the node software. After upgrade, you uncordon the node to bring it back into service. The cluster version updates only after nodes are upgraded and ready. This prevents downtime and keeps the cluster stable. Different strategies like in-place, blue-green, or canary upgrades exist, but all require careful node management and verification.