add simple cost analysis

Signed-off-by: Jason Hall <jason@chainguard.dev>

iac/cost.md

@@ -0,0 +1,49 @@
+# Minimum Cost
+
+Based on the configured resources, estimated minimum monthly cost with no traffic:
+
+GKE Autopilot:
+
+- 1 pod with 100m CPU / 128Mi RAM: ~$3-5/month (Autopilot charges for actual pod resources)
+
+LoadBalancer Service:
+
+- TCP LoadBalancer with forwarding rules: ~$18-22/month (Google Cloud Load Balancer pricing)
+
+Cloud Run:
+
+- Minimal idle cost for 1 CPU/2GB instance: ~$0-2/month (only charges when processing requests)
+
+Other resources (minimal cost):
+
+- DNS zone and records: ~$0.50/month
+- Secret Manager: ~$0.18/month (6 secrets)
+- Container Registry storage: ~$0.10/month
+
+Total estimated minimum cost: ~$22-30/month
+
+The LoadBalancer is the largest cost component at ~75% of the total. The GKE Autopilot pod and Cloud Run service are relatively efficient for small workloads, but the dedicated TCP LoadBalancer has a fixed monthly cost regardless of traffic volume.
+
+# Usage Cost
+
+Cloud Run per-second costs:
+
+- CPU: 1 vCPU × $0.00002400/vCPU-second = $0.000024/second
+- Memory: 2GB × $0.00000250/GB-second = $0.000005/second
+- Total: ~$0.000029/second per Cloud Run instance
+
+Per-80-user cost:
+
+- Assuming each instance handles ~80 concurrent chess games
+- Cost per user-second: $0.000029 ÷ 80 = ~$0.00000036/user-second
+- Cost per user-minute: ~$0.000022/user-minute
+- Cost per user-hour: ~$0.0013/user-hour
+
+Example scenarios:
+- 80 users playing for 10 minutes: ~$0.018
+- 160 users (2 instances) for 30 minutes: ~$0.11
+- 800 users (10 instances) for 1 hour: ~$1.04
+
+The chess game's real-time nature means users stay connected for entire game durations (typically 10-60 minutes), making this quite cost-effective at ~$0.0013 per user per hour of gameplay.
+
+On the other hand, a consistently active user would cost ~$0.94/user/month, so if this got popular and garnered 1M active users 24/7, it would cost $940k. So, that's something to think about...