All the metrics for a particular instance IP:9100 can be obtained via the following PromQL query:

{instance="IP:9100"}

This query returns all the metrics, which have the given instance="IP:9100" label. See time series selector docs for more details. See also PromQL tutorial.

The {instance="IP:9100"} query can be sent to the following Prometheus querying APIs:

• /api/v1/query - this endpoint returns matching time series values at the given timestamp specified via time query arg. For example, curl 'http://prometheus:9090/api/v1/query?query={instance="IP:9100"}' . Make sure you properly encoded query arg with percent encoding. See this demo.
• /api/v1/series - this endpoint returns matching time series without any data, e.g. only metric names and labels are returned. For example, curl 'http://prometheus:9090/api/v1/series?match[]={instance="IP:9100"}'. Make sure you properly encoded match[] arg with percent encoding. See this demo
• /api/v1/query_range - this endpoint returns calculated datapoints for matching time series on the selected time range [start ... end] with the given step interval between samples. See more details about calculated datapoints in these docs.

If you want returning just unique metric names without labels, then you can query /api/v1/label/__name__/values endpoint: curl http://prometheus:9090/api/v1/label/__name__/values . The __name__ is a special label name used in Prometheus for referring to metric names. Note that multiple time series may share the same metric name. For example, http_requests_total{path="/foo"} and http_requests_total{path="/bar"} time series share http_requests_total metric name, while they differ by path label values.

Performing a GET request at <prom-server-ip>:9090/metrics returns the Prometheus metrics (not in JSON format) of the Prometheus server itself.

Since you're trying to perform query, you need to use the HTTP API endpoints like /api/v1/query or /api/v1/query_range instead of using /metrics.

$ curl 'http://localhost:9090/api/v1/query?query=up&time=2015-07-01T20:10:51.781Z'
{
   "status" : "success",
   "data" : {
      "resultType" : "vector",
      "result" : [
         {
            "metric" : {
               "__name__" : "up",
               "job" : "prometheus",
               "instance" : "localhost:9090"
            },
            "value": [ 1435781451.781, "1" ]
         },
         {
            "metric" : {
               "__name__" : "up",
               "job" : "node",
               "instance" : "localhost:9100"
            },
            "value" : [ 1435781451.781, "0" ]
         }
      ]
   }
}

For more detailed information visit Prometheus official docs.

#!/usr/bin/env python

import requests

prome_sql = "(node_memory_MemTotal_bytes - (node_memory_MemFree_bytes + node_memory_Buffers_bytes + node_memory_Cached_bytes)) / node_memory_MemTotal_bytes * 100"

response = requests.get('http://192.168.20.249:9090/api/v1/query',
    params={'query': prome_sql})
print(response.json()["data"]['result'])