manage-builders errors out

[Matthias Klose]

$ ./manage-builders --manual -a i386 -a amd64
Updating 90 builders.
* lcy01-amd64-001
* lcy01-amd64-002
* lcy01-amd64-003
* lcy01-amd64-004
* lcy01-amd64-005
* lcy01-amd64-006
* lcy01-amd64-007
* lcy01-amd64-008
* lcy01-amd64-009
* lcy01-amd64-010
* lcy01-amd64-011
* lcy01-amd64-012
* lcy01-amd64-013
* lcy01-amd64-014
* lcy01-amd64-015
* lcy01-amd64-016
* lcy01-amd64-017
* lcy01-amd64-018
* lcy01-amd64-019
* lcy01-amd64-020
* lcy01-amd64-021
* lcy01-amd64-022
* lcy01-amd64-023
* lcy01-amd64-024
* lcy01-amd64-025
* lcy01-amd64-026
* lcy01-amd64-027
* lcy01-amd64-028
* lcy01-amd64-029
* lcy01-amd64-030
* lgw01-amd64-001
* lgw01-amd64-002
* lgw01-amd64-003
* lgw01-amd64-004
* lgw01-amd64-005
* lgw01-amd64-006
* lgw01-amd64-007
* lgw01-amd64-008
* lgw01-amd64-009
* lgw01-amd64-010
* lgw01-amd64-011
* lgw01-amd64-012
* lgw01-amd64-013
* lgw01-amd64-014
* lgw01-amd64-015
* lgw01-amd64-016
* lgw01-amd64-017
* lgw01-amd64-018
* lgw01-amd64-019
* lgw01-amd64-020
Traceback (most recent call last):
  File "./manage-builders", line 260, in <module>
    candidate.lp_save()
  File "/usr/lib/python2.7/dist-packages/lazr/restfulclient/resource.py", line 776, in lp_save
    URI(self.self_link), representation, headers)
  File "/usr/lib/python2.7/dist-packages/lazr/restfulclient/_browser.py", line 489, in patch
    'PATCH', extra_headers=extra_headers)
  File "/usr/lib/python2.7/dist-packages/lazr/restfulclient/_browser.py", line 431, in _request
    raise error
lazr.restfulclient.errors.PreconditionFailed: HTTP Error 412: Precondition Failed
Response headers:
---
content-length: 0
content-type: text/plain
date: Sun, 06 May 2018 20:36:38 GMT
server: zope.server.http (HTTP)
status: 412
strict-transport-security: max-age=15552000
vary: Accept
x-content-type-options: nosniff
x-content-type-warning: guessed from content
x-frame-options: SAMEORIGIN
x-launchpad-revision: 18623
x-lazr-notifications: []
x-powered-by: Zope (www.zope.org), Python (www.python.org)
x-xss-protection: 1; mode=block
---
Response body:
---

---

[Colin Watson (cjwatson)]

That happens when the state of the builder changes in some way between the object being fetched and the call to .lp_save(). manage-builders needs to cope with this (perhaps e.g. refreshing the object and retrying) and currently doesn't.