19. Application Deployment Strategies on Kubernetes

Introduction

In the world of software, change is a constant. Whether fixing bugs, adding features, or scaling to meet demand, deploying new versions of your applications is essential. While simple in a development environment, deploying changes to live production systems demands careful consideration. Downtime, failed updates, and frustrated users are not an option!

Kubernetes provides powerful tools for orchestrating application deployments in ways that prioritize both safety and efficiency. Gone are the days of risky "all at once" updates. Let's explore strategies designed to minimize disruption while ensuring your application updates roll out smoothly.

Rolling Updates: The Workhorse of Kubernetes Deployments

We'll begin our in-depth look at deployment strategies with rolling updates. This approach is frequently the default in Kubernetes due to its balance of safety and simplicity.

At the core of a rolling update lies the idea of gradual progress. Instead of replacing all your application's pods at once, a rolling update replaces them in a controlled sequence, ensuring your application remains partially available throughout the process.

Key Concepts

• maxSurge and maxUnavailable: These parameters within your Deployment specification control how the rollout progresses. One option is to add new pods before removing old ones ('maxSurge'), another is to specify a max number of pods that can be down at once ('maxUnavailable').

• Health Checks: Kubernetes monitors your pods. Rolling updates only progress if newly launched pods pass readiness and liveness probes.

Advantages of Rolling Updates

• Minimized Downtime: Your application never completely vanishes during the process.

• Graceful Traffic Shifts: Incoming traffic is gradually shifted to new pods as they are ready.

• Automated Rollbacks (Potential): If Kubernetes health checks fail on new pods, rollbacks can be triggered (this gets more advanced).

Blue/Green Deployments

The premise of Blue/Green deployments is straightforward: you maintain two parallel but separate environments.

• Blue: This is your currently active production environment serving live user traffic.

• Green: This is the inactive environment where you deploy the new version of your application.

The Cutover

Once the Green environment is fully deployed, tested, and ready to go, you switch all user traffic from Blue to Green in a single atomic operation. This is typically done by reconfiguring a load balancer or DNS.

Advantages of Blue/Green

• Fast Rollback: If the new version in Green has severe issues, you simply switch traffic back to Blue, restoring the previous working state nearly instantly.

• Testing in Production: You can fully stage and test the new version in a production-like environment without risking user impact before the cutover.

Considerations

• Resource Cost: You temporarily need infrastructure capable of running both environments simultaneously.

• Database Migrations: Often a major complexity if the new version requires schema changes. Tools or planned downtime might be involved here.

Blue/Green is best suited for major overhauls, risky changes, or strict rollback requirements. The added overhead may not be justified for frequent small updates.

Canary Deployments

Named after the practice of miners using canaries to detect dangerous gases, canary deployments expose controlled portions of user traffic to your new application version. This allows you to observe its behavior in a real-world context, gathering metrics and feedback before proceeding with a full rollout.

How It Works:

1. Partial Deployment: You deploy the new version alongside the old, but only a small percentage of traffic is directed to the new pods.

2. Monitoring: Metrics, user feedback, and error logs are closely analyzed to spot issues early.

3. Scaled Release (If Successful): Gradually increase the traffic percentage to the new version. If issues arise, easily roll back to the previous stable version.

GKE's ability to fine-tune traffic distribution, combined with advanced Ingress controllers, enables sophisticated canary release setups.

Advantages

• Minimized Risk: Issues are caught before affecting a vast base of users.

• Data-Driven Decisions: Monitoring helps validate that the new version performs as expected under real-world load.

• Flexibility: Easily adjust the percentage of traffic exposed to the 'canary'.

Canary deployments are great for:

• High-risk or critical changes where gradual rollout is desired.

• Testing new features with a subset of users to gather feedback.

When to choose which deployment strategy

Outro

We've explored safer deployment paths! But safety extends beyond rollouts. Next, we conquer secrets management using GCP Secret Manager, ensuring sensitive data is never exposed within your Kubernetes environments.