Fan-out inline in the request path

warningfanout-inline-in-request-path

Calling a worker synchronously puts the background job on the request path. The caller waits for the slowest part of the fan-out.

Severity: warning
Selects: every node of kind app-server
Components in scope: 99

What it checks

It looks at every node of kind app-server, and fires when:

— the node has at least one synchronous outgoing edge to a worker

Message

Service '{{node.id}}' calls a worker synchronously. Hand the job to a queue or stream so the request path does not wait for fan-out.

{{node.id}} style paths are filled in from the node, the edge or the design the finding is about.

Applies to · 99 components

Application server app-server

Tripped by · 15

Reference designs whose broken twin names this rule in its header. The gate reads the same header, and fails when a rule no design trips.

airbnb-searchreference amazon-orderreference canva-uploadsreference datadog-huskyreference duolingo-backendreference github-mysqlreference hotstar-streamingreference khan-academy-goliathreference linear-syncreference notion-shardingreference paypal-paymentsreference pinterest-feedreference stock-exchangereference twitter-timelinereference youtube-upload-playbackreference

Source

1# yaml-language-server: $schema=../schema/rule.schema.json
2# An app-server that calls a worker synchronously puts fan-out (or any background job) on the
3# request path: the caller's latency becomes the tail of the follower distribution.
4# Tripped by: designs/twitter-timeline.broken.yaml
5schemaVersion: "1"
6type: "rule"
7id: "fanout-inline-in-request-path"
8severity: "warning"
9select:
10  node:
11    kind: "app-server"
12when:
13  hasEdge:
14    direction: "out"
15    mode: "sync"
16    peerKind: "worker"
17message: "Service '{{node.id}}' calls a worker synchronously. Hand the job to a queue or stream so the request path does not wait for fan-out."

The same page as markdown, for an agent: /catalogue/rules/fanout-inline-in-request-path.md