Rolling vs Blue-Green for Zero-Downtime Meteor Migration

Rolling vs Blue‑Green for Zero‑Downtime Meteor Migration

Rolling deployment uses a single codebase with dual‑schema support, while blue‑green duplicates the whole environment to avoid schema conflicts.

Likely explanation

The main trade‑off is operational simplicity versus isolation cost. Rolling keeps one server group, requires manual draining of active DDP method calls, and relies on schema version compatibility. Blue‑green runs two identical stacks, switches traffic at the load balancer, and eliminates schema‑drain concerns but adds duplicate infrastructure and higher expense.

Confirmed facts

• Meteor’s DDP lifecycle does not provide built‑in draining of in‑flight method calls; application code must explicitly pause or finish ongoing calls.
• DDP version pinning does not guarantee graceful transition for existing connections; client‑side version handling is required.
• Blue‑green adds duplicate infrastructure and higher operational cost, which may be unnecessary for a small app unless strict isolation is needed.

Steps for a zero‑downtime rolling migration

1. Design dual‑schema migrations so old and new schemas coexist (e.g., add new fields as optional, keep existing queries functional).
2. Instrument a health‑check that reports the number of active DDP connections; use this to pause new method calls and wait for existing ones to complete before cutover.
3. Deploy the new Meteor version while the old schema remains active; monitor DDP connection counts during the rollout.
4. Switch traffic to the new version using your load balancer or router, then gracefully close or redirect the remaining old connections.
5. Run a staged load test that simulates the cutover and verify that no DDP errors appear for in‑flight method calls.
6. Inspect DDP connection logs before and after the switch to confirm graceful closure.

Missing diagnostic detail

Do you have a reliable endpoint or metric that reports active DDP connections at the moment of cutover? This information is needed to confirm that the manual drain step can be performed safely.