dispatch: fix missing receivers in Groups()

[simonpasquier]

Closes #1959

[stuartnelson3]

great idea

[simonpasquier]

It was very much needed for the tests to pass :)

[simonpasquier]

@prymitive can you tell me if it fixes the issue for you?

[prymitive]

I can do some testing after work and update here

[prymitive]

Test using master branch:

$ ./alertmanager --version
alertmanager, version 0.18.0 (branch: HEAD, revision: f450720213de12237437552fa8e86b715e0baafa)
  build user:       lukasz@kwakBook
  build date:       20190723-21:56:49
  go version:       go1.12.7

kwakBook:alertmanager lukasz$ curl -s localhost:9093/api/v2/alerts/groups | jq -c '.[] | .receiver' | sort | uniq -c
   3 {"name":"by-cluster"}
  15 {"name":"by-cluster-service"}
  24 {"name":"by-name"}
kwakBook:alertmanager lukasz$ curl -s localhost:9093/api/v2/alerts/groups | jq -c '.[] | .receiver' | sort | uniq -c
   3 {"name":"by-cluster"}
  15 {"name":"by-cluster-service"}
  24 {"name":"by-name"}
kwakBook:alertmanager lukasz$ curl -s localhost:9093/api/v2/alerts/groups | jq -c '.[] | .receiver' | sort | uniq -c
   3 {"name":"by-cluster"}
  15 {"name":"by-cluster-service"}
  24 {"name":"default"}

There's either default or by-name receiver, but never both, so we hit this issue.

Test using this PR as HEAD:

$ ./alertmanager --version
alertmanager, version 0.18.0 (branch: pr/1964, revision: 110dd7555c254a3409515d1d7289e6833b7acd1a)
  build user:       lukasz@kwakBook
  build date:       20190723-21:45:37
  go version:       go1.12.7

kwakBook:alertmanager lukasz$ curl -s localhost:9093/api/v2/alerts/groups | jq -c '.[] | .receiver' | sort | uniq -c
   3 {"name":"by-cluster"}
  16 {"name":"by-cluster-service"}
  13 {"name":"by-name"}
  13 {"name":"default"}
kwakBook:alertmanager lukasz$ curl -s localhost:9093/api/v2/alerts/groups | jq -c '.[] | .receiver' | sort | uniq -c
   3 {"name":"by-cluster"}
  15 {"name":"by-cluster-service"}
  12 {"name":"by-name"}
  12 {"name":"default"}
kwakBook:alertmanager lukasz$ curl -s localhost:9093/api/v2/alerts/groups | jq -c '.[] | .receiver' | sort | uniq -c
   3 {"name":"by-cluster"}
  16 {"name":"by-cluster-service"}
  13 {"name":"by-name"}
  13 {"name":"default"}

Both receivers are always present as expected, so the issue is gone.

[fcastello]

Can it be that this issue was not fully fixed?
I am still seeing duplicates when I add multiple receivers

    - match:
        destination: webhook
      receiver: webhook
      continue: true
    - match:
        destination: webhook
      receiver: slack

That is the part of my config that generates the duplicate alerts in the UI, Also they are inheriting the group_by from the main config.
I am running the image with master tag from dockerhub which states that was built 2 days ago so this fix should be in there

[simonpasquier]

@fcastello can you share a screenshot and the full AlertManager configuration? I tried to reproduce but couldn't spot the issue.