Presentation of Consul Service Discovery for use-case in Alice O2 Quality Control and its Information Service. How to use Consul to share states of published data by processes.

1. Consul
Service discovery
Vladimir Kosmala
vladimir.kosmala@cern.ch
1

2. • Consul overview
• O2 requirements
• Quality Control usecase
• Prototype
• Conclusion
!2
Outline

3. Consul overview
• Service discovery
• Health checking
• KV store
• Distributed
3

4. Consul overview
• Config file
• HTTP API
• DNS
• CLI
• Web GUI
4

5. !5
Checklist O2 requirements
- provide API
- track status of services
- read status of services
- notify on service failure

6. Usecase:
QC Information Service
!6
?
...
agent
object
?
?
central process

7. !7
...
"Service discovery made easy"

8. !8
1. Register Service (once)
QC Information Service
2. Register health check (once)
Agent DAQ, TOF, etc.
3. Publish health status (+ listing)
Objects foo, bar, baz
4. Reading status from Consul
all agents and their objects
Steps for QC

9. curl
http://localhost:8500/v1/agent/service/register
--request PUT
--data '{"name":"information-service"}'
1. Register service

10. curl
http://localhost:8500/v1/agent/check/register
--request PUT
--data '{"name":"daq-agent", "ttl": "6s", "serviceid": "information-service"}
2. Register health check

11. curl
http://localhost:8500/v1/agent/check/update/daq-agent
--request PUT
--data '{"status": "passing", "output": "daq/_Event/trace,daq/_Event/log"}'
3. Publish health status (+ listing)

12. curl
http://localhost:8500/v1/health/checks/information-service
4. Reading status from Consul
[
{
"Node": "vlad",
"CheckID": "daq-agent",
"Name": "daq-agent",
"Status": "passing",
"Notes": "",
"Output": "daq/_Event/trace,daq/_Event/log",
"ServiceID": "information-service",
"ServiceName": "information-service",
"ServiceTags": [],
"Definition": {},
"CreateIndex": 12,
"ModifyIndex": 45
},
{
"Node": "vlad",
"CheckID": "tof-agent",

13. !13
...
"Service discovery made easy"
[
{
"Node": "vlad",
"CheckID": "daq-agent",
"Name": "daq-agent",
"Status": "passing",
"Notes": "",
"Output": "daq/_Event/trace,
"ServiceID": "information-se
"ServiceName": "information-
"ServiceTags": [],
"Definition": {},
"CreateIndex": 12,
"ModifyIndex": 45
},
{
"Node": "vlad",
"CheckID": "tof-agent",
"Name": "tof-agent",
"Status": "critical",
"Notes": "",
"Output": "TTL expired",
"ServiceID": "information-se
"ServiceName": "information-
"ServiceTags": [],
"Definition": {},
"CreateIndex": 13,
"ModifyIndex": 42
}
]

14. !14
ok!
1. Register Service (once)
QC Information Service
2. Register health check (once)
Agent DAQ, TOF, etc.
3. Publish health status (+ listing)
Objects foo, bar, baz
4. Reading status from Consul
all agents and their objects
Steps for QC

15. Checklist O2 requirements
- provide API
- track status of services
- read status of services
- notify on service failure
!15

16. Notify on service failure
with "Consul watches"
Start command and add
notification handlers:
• http handler
POST http://QC.cern.ch
• command handler
/usr/bin/infologger
16

17. 17
consul watch -type=service -service=information-service /bin/cat
Notify on service failure
with "watches"
[...]"Name":"tof-agent","Status":"passing"[...]
[...]"Name":"tof-agent","Status":"critical"[...]
ttl => 6s
POST status

18. !18
Checklist O2 requirements
- provide API
- track status of services
- read status of services
- notify on service failure

19. !19
# names are required
# ids are names by default, must be unique
# list services
curl http://localhost:8500/v1/agent/services
# put one service
curl http://localhost:8500/v1/agent/service/register --request PUT --data '{"name":"information-service"}'
# put check
curl http://localhost:8500/v1/agent/check/register --request PUT --data '{"name":"daq-agent", "ttl": "6s", "serviceid":
"information-service"}'
curl http://localhost:8500/v1/agent/check/register --request PUT --data '{"name":"tof-agent", "ttl": "6s", "serviceid":
"information-service"}'
# update check status
curl http://localhost:8500/v1/agent/check/update/daq-agent --request PUT --data '{"status": "passing", "output": "daq/
_Event/trace,daq/_Event/log"}'
curl http://localhost:8500/v1/agent/check/update/tof-agent --request PUT --data '{"status": "passing", "output": "tof/
_Compute/map,tof/_Compute/reduce"}'
# list checks passing
curl http://localhost:8500/v1/health/state/passing
# watch changes
consul watch -type=service -service=information-service /bin/cat
Memo