Stateful hash ring without ring manager

warningstateful-hash-ring-without-ring-manager

A stateful service on a consistent hash ring needs something that owns the ring: detect a dead host, pick a replacement, tell everyone. Without a coordination service the ring is edited by hand during the outage.

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:

— all of these hold:
— the node's `shardingStrategy` is "consistent-hash"
— this does not hold:
— the node has at least one connected edge joining a coordination-service

Message

Service '{{node.id}}' is on a consistent hash ring but is not connected to a coordination service that manages the ring.

{{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 · 9

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.

datadog-huskyreference discord-messagesreference etsy-searchreference facebook-messengerreference grab-georeference slack-messagingreference tinder-georeference twitch-livereference uber-dispatchreference

Source

1# yaml-language-server: $schema=../schema/rule.schema.json
2# A stateful service on a consistent hash ring needs something to own the ring: detect a
3# dead host, pick a replacement and tell everyone. Without a ring manager (a
4# coordination service) the ring is edited by hand during the outage.
5# Tests "this node has no edge to a coordination service" rather than "the design has no
6# coordination service" so it can co-fire with reconnect-stampede-without-guard, which
7# requires one to exist.
8# Tripped by: designs/slack-messaging.broken.yaml
9schemaVersion: "1"
10type: "rule"
11id: "stateful-hash-ring-without-ring-manager"
12severity: "warning"
13select:
14  node:
15    kind: "app-server"
16when:
17  all:
18    - prop: "shardingStrategy"
19      equals: "consistent-hash"
20    - not:
21        hasEdge:
22          direction: "any"
23          peerKind: "coordination-service"
24message: "Service '{{node.id}}' is on a consistent hash ring but is not connected to a coordination service that manages the ring."

The same page as markdown, for an agent: /catalogue/rules/stateful-hash-ring-without-ring-manager.md