3.3.2. Deployment Strategies (In-place, Rolling, Blue/Green)

💡 First Principle: Application deployment strategies manage the risk of introducing new code into production, prioritizing minimal downtime and controlled exposure for reliable releases.

Scenario: You need to deploy a new version of a critical application. You want to ensure minimal downtime during the deployment and have the ability to immediately revert to the previous version if any issues are detected.

For SysOps Administrators, selecting the right deployment strategy is crucial for minimizing disruption to users and ensuring application availability when new code is released. The choice depends on the application's criticality and downtime tolerance.

Key Application Deployment Strategies:

• In-place Deployment: (Updates application directly on existing servers or instances.)
  • How it works: Stops the application on each instance, deploys the new version, and restarts the application.
  • Pros: Simple, consumes minimal resources (no need for extra instances).
  • Cons: Incurs downtime, higher risk if the deployment fails.
• Rolling Update: (Gradually replaces old versions with new ones in a phased manner across a fleet of instances.)
  • How it works: Deploys the new version to a subset of instances at a time, gradually moving through the fleet.
  • Pros: Reduces downtime compared to in-place, maintains some capacity during deployment.
  • Cons: Deployment can be slow, potential for mixed environments (old and new versions running simultaneously), rollbacks can be complex.
• Blue/Green Deployment: (Runs two identical production environments, "Blue" (old version) and "Green" (new version), and shifts traffic when the new version is validated.)
  • How it works: A completely new environment ("Green") is provisioned with the new application version. Once "Green" is fully tested and validated, traffic is shifted from "Blue" to "Green."
  • Pros: Near-zero downtime, instant rollback (switch traffic back to "Blue"), ideal for critical applications.
  • Cons: Requires provisioning double the resources, potentially higher cost.
• Canary Deployment: (Rolls out a new version of an application to a small percentage of users first, then gradually to all users if it performs well.)
  • Pros: Minimizes impact of issues to a small subset of users, real-world testing.
  • Cons: More complex to implement traffic shifting and monitoring.

⚠️ Common Pitfall: Choosing a deployment strategy that doesn't align with the application's downtime tolerance or criticality (e.g., using in-place for a critical production app).

Key Trade-Offs: Downtime (in-place) vs. cost (Blue/Green requires more resources) vs. complexity (Canary).

Reflection Question: How do deployment strategies like Blue/Green and Rolling updates, by managing the risk of introducing new code into production, prioritize minimal downtime and controlled exposure for reliable application releases?