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+# RFC 139 - Increase identifier length from 20 to 44
+* Comments: [#139](https://api.github.com/repos/taskcluster/taskcluster-rfcs/pull/139), [Bug 1520579](https://bugzilla.mozilla.org/show_bug.cgi?id=1520579)
+* Proposed by: @djmitche / @mitchhentges
+
+# Summary
+
+For identifiers that typically contain structure (vs. those containing only
+slugid's), increase the maximum length from 22 to 40 characters, while ensuring
+that we do not overflow AMQP routing key lengths.
+
+## Motivation
+
+We have an established pattern of encoding meaning into some identifiers, such as workerTypes (e.g., `aws-provisioner-v1/gecko-1-b-*`), but these are limited to 22 characters.
+That is too short to encode much meaning.
+We cannot allow arbitrary lengths, as these identifiers are included in AMQP routes which have a hard limit of 255 characters.
+We can, however, allow more than 22 characters.
+
+# Details
+
+We will define two types of identifiers:
+
+* "identifiers" -- up to 40 characters, generally containing human-readable identifiers
+  * `provisionerId`, `workerType`, `workerGroup`, `workerId`
+  * `schedulerId`
+  * `organization`, `repository` (in tc-github)
+
+* "slugids" -- exactly 22 characters, always a slugid
+  * `taskGroupId`
+  * `taskId`
+
+This change requires changes to schemas and API declarations in services in the monorepo, as well as to `aws-provisioner` and possibly `ec2-manager`, workers, and client libraries.
+Much of this work has [already been done](https://github.com/taskcluster/taskcluster/pull/110) by @OjaswinM.
+
+We already have checks on AMQP routing key lengths, and the increased length does not cause any failures in that code.
+
+# Open Questions
+
+TBD
+
+# Implementation
+
+* https://github.com/taskcluster/taskcluster/pull/110
+* TBD