infra(app): one nginx instance, concurrency 80

[MarkusNeusinger]

Summary

• anyplot-app runs as a single instance with concurrency 80 (was max 3, concurrency 15; min-instances stays 0). A static nginx never needed a second instance for capacity — its files answer in milliseconds and it sits at 15 MiB p99 of 512Mi — yet every crawler burst filled the 15 slots and started one or two more instances (50 AUTOSCALING starts in the ten days to 2026-09-10), because nginx holds a proxied bot request open for as long as the API takes to answer. One forged-UA burst on 2026-09-09 filled the instance and started two more. With the API on one warm instance (infra(api): single instance, non-blocking prewarm, OG renders off the loop #11828) those waits are milliseconds, and one nginx with 80 slots absorbs the burst without a 0.26 s cold start.
• Owner decision 2026-09-11: one instance per service in both projects (the sibling PR in kurrentschrift does the same there). If 429s ever appear, max 2 is the next step.
• docs/reference/performance.md still says max 3 / concurrency 15 for the frontend after this PR: infra(api): single instance, non-blocking prewarm, OG renders off the loop #11828 edits the same table row, so the row is updated in a follow-up once both have merged, to keep the two PRs from conflicting.

Plan

N/A — measurements in the Todoist task "Nachprüfen: merkt jemand, dass anyplot-app auf null skaliert?" (closed 2026-09-10 with the numbers) and in #11828.

Test plan

• app/cloudbuild.yaml parses; the deploy step carries --min-instances 0 --max-instances 1 --concurrency 80
• uv run python -m tools.changelog check --base origin/main passes
• No image or nginx change: the app image and the origin-gate smoke in CI are unaffected; the candidate smoke in Cloud Build probes the new revision before traffic moves
• After merge: Cloud Build deploy-app green; gcloud run revisions describe on the promoted revision shows maxScale 1, containerConcurrency 80; then two weeks of run.googleapis.com/request_count by response_code (zero 429s expected) and instance-start logs (AUTOSCALING starts should stop)

🤖 Generated with Claude Code

https://claude.ai/code/session_01CELiZYpFBQc5bncjWXYrue

[Copilot]

🔵 Needs a closer look

The production capacity and deployment configuration change requires final human review.

Pull request overview

Caps the frontend Cloud Run service at one instance and raises concurrency to 80.

Changes:

• Sets max-instances to 1 and concurrency to 80.
• Documents the operational rationale in configuration and changelog.

File summaries

File	Description
app/cloudbuild.yaml	Updates Cloud Run scaling settings.
changelog.d/app-single-instance.md	Records the infrastructure change.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

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✅ All modified and coverable lines are covered by tests.

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