Architecture Case Study: Migrating a Developer SaaS from Serverless to a $10 VPS with Docker
Serverless platforms like Vercel and AWS Lambda are the default choice for modern web applications. For the first few months of building our developer platform, the serverless promise held up: push to
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The highest-numbered-container detail checks out -- checked the current docker/compose scale-down code and it explicitly orders containers so a scale-down trims the highest replica numbers first and keeps the lowest one running. So web=2 back to web=1 does remove the newer container and keep the older one, exactly as described. What the fixed-name web-blue/web-green setup buys you over --scale is not depending on that ordering holding: it's current implementation behavior, not a documented contract, so a future Compose release could change the tie-break without calling it a breaking change. Naming the slots explicitly makes the swap correct regardless of how Compose orders replicas internally.