What Is the Best Update Strategy for a Node.js App on GCP: MIG or App Engine?

Below is an outline of the common practices and considerations based on industry best practices for updating applications in a Managed Instance Group (MIG) and how that might compare with an App Engine deployment:

Updating Your MIG Application

There are two common approaches to deploy updates to your MIG:

1. Image Template with Startup Script:
   • How It Works: Each time an instance launches (or resumes from a scaling event), a startup script runs that pulls the latest code from GitHub, installs dependencies, builds, and runs the app.
   • Pros & Cons:
     • Pros:
       • Flexibility to always get the latest code.
       • Avoids rebuilding new images for each update.
     • Cons:
       • Dependency on runtime availability of source code and build tools.
       • Possibility of inconsistency if the startup script experiences temporary failures or if external dependencies change.
2. Immutable Infrastructure via Versioned Images:
   • How It Works: You create an instance, configure it with the correct version, and then convert that configured instance into an image, which is then used in the MIG. For updates, you create a new image and update the instance template, triggering a rolling update.
   • Pros & Cons:
     • Pros:
       • Ensures all instances start from a known state, reducing build-time variability.
       • Rolling update strategies can be managed reliably (e.g., blue/green or canary releases).
     • Cons:
       • Requires the extra step of baking a new image for each update.
       • May add overhead to the release process if image builds are slow.

Best Practice Recommendation:
For production environments, the immutable image approach is generally preferred. It provides consistency across your instances and minimizes the risk of runtime errors during startup. By using rolling updates with a versioned instance template, you can achieve smoother deployments and easier rollbacks if necessary.

MIG vs. App Engine Based on Budget Considerations

Since your app is stateless, but relies on an external MongoDB instance, here are some points to consider:

• Managed Instance Group (MIG):

  • Flexibility: Offers full control over the VM configuration and environment.
  • Cost Considerations: Can be optimized, but you need to take into account the cost of the VMs, persistent disks, and any associated networking overhead—even during low traffic periods.
  • Management Overhead: You must manage scaling, instance health, and updates manually (albeit through rolling updates).

• App Engine:

  • Simplicity: Offers built-in auto scaling with less configuration overhead.
  • Cost Efficiency: Often more cost-effective for stateless applications, particularly when traffic is low—as you pay strictly for what you use.
  • Operational Overhead: Reduces the burden of managing underlying infrastructure, which can be beneficial when operating within a strict budget.

Budget and Usage Context:
Given your budget cap of approximately 300 USD/month, and that you typically operate at 50-60% of that capacity during low traffic, App Engine tends to offer a simpler and often more cost-efficient solution. The platform’s auto scaling charges align well with lower traffic periods, helping optimize spend, whereas MIG might incur fixed costs even when usage is minimal.

Conclusion

• For MIG Updates: The immutable image approach (baking your application into a new instance image and updating your instance template) is recommended for production, as it provides consistency, reduces runtime errors, and integrates well with rolling update strategies.

• For Deployment Based on Budget: If minimizing management overhead and cost is a priority, and your application is stateless (except for the MongoDB dependency), App Engine is often the better option under a limited budget scenario.

These recommendations focus on producing reliable and predictable deployments while keeping cost and operational overhead in check.