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Blue-Green Deployment Calculator

Calculate resource and downtime implications of a blue-green deployment switch.

About Blue-Green Deployment Calculator

A blue-green deployment keeps both the old (blue) and new (green) environments fully provisioned simultaneously during the cutover window, so peak resource usage doubles: resources = 2 × normal. Rollback speed is bounded by how quickly traffic can be redirected back to the stable environment, which for DNS-based cutovers is governed by the DNS record's TTL plus a buffer for resolvers/clients that cache slightly beyond the nominal TTL: rollback_time = dns_ttl + propagation_buffer.

Formula

total_capacity_during_deploy = blue_instances + green_instances

blue_instances
Instances in the current (blue) environment
green_instances
Instances in the new (green) environment

Worked example

With the default values below, Blue-Green Deployment Calculator returns Peak CPU During Cutover of 40.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Normal CPU Usageaccepts 0–1,000,000 cores
20 cores
Normal Memory Usageaccepts 0–10,000,000 GiB
80 GiB
Cutover Window Durationaccepts 0–100,000 minutes
30 minutes
DNS/Routing TTLaccepts 1–604,800 seconds
60 seconds
Propagation Bufferaccepts 0–100,000 seconds
30 seconds

Results

Peak CPU During Cutover
40.0 cores
Peak Memory During Cutover
160.0 GiB
Expected Rollback Time
1.50 minutes
Extra CPU Needed
20.0 cores
Extra Memory Needed
80.0 GiB

Step by step

  1. 1Peak CPU during cutover: 2 × normal= 40 cores
  2. 2Peak memory during cutover: 2 × normal= 160 GiB
  3. 3Rollback time: DNS TTL + propagation buffer= 90s (1.50 min)

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does blue-green require double the resources?

Unlike a rolling update which replaces capacity incrementally, blue-green provisions a complete second environment before cutting over, so both environments must run at full capacity simultaneously during the overlap window to allow instant, safe rollback.

How can I reduce the doubled resource cost?

Shorten the cutover window duration (validate quickly and decommission the old environment sooner), or use a partial blue-green approach where only a subset of capacity is duplicated while traffic gradually shifts — though this starts to resemble a canary deployment.

Why does DNS TTL matter for rollback speed if I'm using a load balancer?

If cutover is done via DNS record changes (e.g. pointing a CNAME to a new load balancer), rollback speed is bounded by DNS TTL and caching resolvers; if cutover is done via a load balancer's own routing rules or service mesh virtual service, rollback can be nearly instant instead, bypassing DNS propagation delay entirely.

What's a safe propagation buffer beyond the nominal TTL?

20-50% of the TTL value is a reasonable buffer to account for resolvers and clients that don't strictly honor TTL, though some misbehaving clients or aggressive caching layers (e.g. some corporate proxies) can hold stale records far longer than the TTL suggests.

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Blue-Green Deployment Calculator | Calcrivo