Http

Sometimes, you may need to query variables from datasources other than we already provided.

In these cases, you should make a http request and parse the response data to get the variable values you want.

In this doc, we will make http request to jaeger to get its operation under frontend service.

Before start, you should have a Jaeger instance running, refer to https://www.jaegertracing.io/ for more info.

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Create http datasource

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Create http Variable

Let’s create a variable named operation to query data from jaeger http api:

http://localhost:16686/api/services/frontend/operations

We will use service variable created in Jaeger doc, please make sure it still exists.

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Basic info

First fill in the variable editor with:

You should have noticed, we have use a service variable in Query values field:

http://localhost:16686/api/services/${service}/operations

which means we can use variable in HTTP request url.

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Edit request

In Request transform section, we can set params for http request, such as start time, end time etc.

You can’t use variable format in function body, but you can use its variables param instead.

As we don’t need any params for this request, just leave it as default.

If you look into the Request transform function, you should see it default add start and end params to you request.

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Edit response

This is the most important part of HTTP datasource, we need to parse the response data to get the variable values we want.

Response transform function must return a object as below:

{
    "error": null,
    "data": ['value1', 'value2']
}

As we already know this http request will return :

{
  "data": [
    "/logproto.Querier/Label",
  ],
  "total": 31,
  "limit": 0,
  "offset": 0,
  "errors": null
}

so Let’s modify this function to :

function transformResult(httpResult) {
    return {
        error: httpResult.errors,
        data: httpResult.data
    }
}

Now we can successfully get the operation variable values with service variable set to frontend :

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Final result

This is easy just because the response of jaeger api is already in the format we want, but in most cases, you need to do some extra work to get the variable values you want.

As you can see, because we use service variable in Http request url, when we change the service variable value, the operation variable values will change accordingly, great!