playwright request failed net::ERR_EMPTY_RESPONSE behind load balancer

TL;DR

The load balancer closed the connection without answering, usually because the backend was deregistered, the idle timeout fired, or the request hit a dead pool member. Check LB target health first, then align keep-alive and idle timeouts between Playwright and the LB. If the origin is healthy and the LB still empties responses, the LB config is the bug.

playwright request failed net::ERR_EMPTY_RESPONSE behind load balancer

Use this when

• The error appears only through the load balancer, never direct to origin.
• Failures cluster after idle periods or during deploys.
• The LB is AWS ALB/NLB, GCP, Cloudflare, or nginx/haproxy.

Not for this skill when

• Direct-to-origin requests also fail. That is the backend, not the balancer.
• The error is ERRCONNECTIONRESET. That is a reset, a different failure.

Steps

1. Check the LB target health: every backend should be healthy at the moment of failure. Verify: no targets flapping or draining during the failure window.
2. Compare idle timeouts: the LB's idle timeout must exceed the longest gap between requests on a reused connection. Verify: raising the LB idle timeout (e.g. ALB 60s default) stops the failures.
3. Disable connection reuse for the test: new Playwright context per batch. Verify: failures disappear, confirming stale pooled connections through the LB.
4. Check sticky sessions: if the app needs stickiness and the LB routes to a dead member, the response empties. Verify: stickiness settings match what the app expects.
5. During deploys, confirm connection draining is enabled with a drain timeout longer than in-flight requests. Verify: deploys stop producing empty responses.

Variant phrasings

ERREMPTYRESPONSE load balancer

The short search, same LB-first diagnosis.

playwright empty response alb

Vendor phrasing, points at the idle-timeout check.

load balancer closes connection no response

Symptom phrasing, lands on step 1.

Compatibility: Playwright 1.x, any LB. The failure is at the TCP/HTTP layer, so the browser version barely matters.

Why it happens

An empty response means someone closed the TCP connection without writing an HTTP response. Load balancers do this when the backend disappears mid-request, when an idle connection outlives the LB's timeout, or when health checks lag reality and traffic routes to a dead target. The browser cannot distinguish these; only the LB's logs can.

Edge cases / pitfalls

• Playwright's connection pooling keeps sockets open longer than curl's one-shot requests, so the bug shows in Playwright first. That does not make it a Playwright bug.
• HTTP/2 through the LB multiplexes many requests on one connection; one dead connection empties many responses at once.
• Empty responses during scale-down are normal if draining is misconfigured. Fix the drain, not the client.
• Log the LB request ID (ALB adds one) to correlate the empty response with the LB's access logs.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_HUDXJaSSFRGeEbVm1qnVXg