Rolling update strategy in Kubernetes - Step-by-Step Execution

Process Flow - Rolling update strategy

Start with current version pods

↓

Create new version pods gradually

↓

Wait for new pods to be ready

↓

Delete old version pods gradually

↓

Check if all pods are updated

↓

Continue update

The rolling update replaces old pods with new ones step-by-step, ensuring availability by creating new pods before deleting old ones.

Execution Sample

Kubernetes

kubectl set image deployment/myapp myapp=nginx:2.0
# Rolling update starts
kubectl rollout status deployment/myapp

This command updates the image of the deployment 'myapp' to version 2.0 and monitors the rolling update progress.

Process Table

Step	Action	Pods Old Version	Pods New Version	Status	Notes
1	Start rolling update	3	0	Old version running	All pods running old version
2	Create 1 new pod	3	1	New pod starting	New pod created, old pods still running
3	Wait for new pod ready	3	1	New pod ready	New pod passed readiness checks
4	Delete 1 old pod	2	1	Old pod terminated	One old pod removed
5	Create 1 new pod	2	2	New pod starting	Second new pod created
6	Wait for new pod ready	2	2	New pod ready	Second new pod ready
7	Delete 1 old pod	1	2	Old pod terminated	Another old pod removed
8	Create 1 new pod	1	3	New pod starting	Third new pod created
9	Wait for new pod ready	1	3	New pod ready	Third new pod ready
10	Delete last old pod	0	3	Old pods terminated	All old pods removed
11	Update complete	0	3	All pods running new version	Rolling update finished

💡 All old pods replaced by new pods, update complete

Status Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	After Step 8	After Step 10	Final
Pods Old Version	3	3	2	2	1	0	0
Pods New Version	0	1	1	2	3	3	3
Status	Old version running	New pod starting	Old pod terminated	New pod ready	New pod starting	Old pods terminated	All pods running new version

Key Moments - 3 Insights

Why do we create new pods before deleting old pods?

Creating new pods first ensures the application stays available during the update, as shown in steps 2 and 3 where new pods start and become ready before old pods are deleted in step 4.

What happens if a new pod is not ready?

The update pauses until the new pod passes readiness checks, preventing deletion of old pods and avoiding downtime, as seen in the 'Wait for new pod ready' steps (3, 6, 9).

How do we know when the rolling update is complete?

When all old pods are deleted and all pods run the new version, as in step 11 where old pods count is 0 and new pods count is 3.

Visual Quiz - 3 Questions

Look at the execution table, how many new version pods exist after step 6?

A 3

B 1

C 2

D 0

💡 Hint

Check the 'Pods New Version' column at step 6 in the execution table.

At which step does the first old pod get deleted?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Look for the first 'Old pod terminated' status in the execution table.

If new pods took longer to become ready, which step would be delayed?

A Creating new pods

B Deleting old pods

C Starting rolling update

D Update complete

💡 Hint

Refer to the 'Wait for new pod ready' steps before old pods are deleted.

Concept Snapshot

Rolling update strategy in Kubernetes:
- Gradually replace old pods with new pods
- Create new pods first, wait until ready
- Then delete old pods step-by-step
- Ensures zero downtime during updates
- Use 'kubectl set image' and 'kubectl rollout status' to manage

Full Transcript

The rolling update strategy in Kubernetes updates application pods gradually to avoid downtime. It starts by creating new pods with the updated version while keeping old pods running. Once new pods are ready, old pods are deleted one by one. This cycle repeats until all pods run the new version. Commands like 'kubectl set image' trigger the update, and 'kubectl rollout status' monitors progress. This method ensures continuous availability during updates.