These kinds of errors are going to happen in production, whether you inject them or let them occur naturally. Any release process that doesn't go perfectly with a drain / rebalance / start new version / rebalance per (backend, proxy) combo is going to have a timeout or broken connection between the proxy and the backend as it restarts. Should you return 502 to your users when that happens? Nope, just retry on a different backend. This lets you test that.