Consul Health Checks and Service Deregistration

[Mark Selby]

Below is a contrived example of one of the checks that we run for a service.

As we know when the health check fails we can query this status via the API

Right now we are telling out developers in order to use Consul for services you need to perform two steps

1. lookup the service via /v1/catalog/service
2. check its health via /v1/health/service

We use tags pretty heavily so we need to use the /v1/catalog/service API in order to filter by the tag set we need.

What we really want is for services to deregister themselves after a certain number of health checks fail and then re-enable when they come back. We have played with "deregister_critical_service_after": "1m" but that leads to longish de-registration time and no automatic re-registration.

My question is really this. Is the two process the "accepted" practice in terms of connecting to healthy services or is there some other paradigm that can be followed to get the behavior we desire.

Thansk!

{

  "service": {

    "name": "influxdb",

    "tags": ["generic","prod","generic-prod"],

    "address": "10.123.14.131",

    "port": 8086,

    "enableTagOverride": false,

    "checks": [

      {

        "tcp": "localhost:8086",

        "interval": "10s",

        "timeout": "1s",        

      }

    ]

  }

}

[JD Harrington]

Hi Mark :)

You can query the health endpoint with a “tag” parameter and also a “passing” parameter.

https://www.consul.io/docs/agent/http/health.html#health_service

So, you’d probably want to query something like:

/v1/health/service/influxdb?tag=generic-prod&passing

I don’t think, however, that you can currently filter on multiple tags this way, so maybe that’s why it’s necessary for you to use the catalog API.

You could look at prepared queries as an alternative:

https://www.consul.io/docs/agent/http/query.html

Hope that helps!

- JD

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[JD Harrington]

Also, the /v1/health/service/<service> endpoint returns the tags as well, so you should be able to call it with ?passing and then filter by tag set while saving yourself the call to the Catalog API.

[Mark Selby]

Your suggestion will work for me. you can not query by multiple tags in any aspect without prepared queries so this is not a limitation of the health API.

Thanks very much !

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