Prometheus client transport has no TLS options

[coderigo]

Specifying a prometheus server in the config as described in the docs does not allow setting any TLS configs and hitting prometheus servers with self-signed certificates or that require client auth fails.

The suggestion would be to update a given server block's config settngs to accept a tls config block like this:

prometheus "$name" {
  uri         = "https://..."
  failover    = ["https://...",...]
  tags        = ["...",...]
  headers     = { "..." : "..." }
  timeout     = "2m"
  concurrency = 16
  rateLimit   = 100
  required    = true | false
  include     = ["...",...]
  exclude     = ["...",...]
  # add TLS settings, leave block empty if no TLS
  tls {
    enabled       = true # default to false
    skipVerify    = true # default to false
    caCert        = "/some/path/to/my/ca.crt"
    clientCert    = "/some/path/to/my/client.crt"
    clientCertKey = "/some/path/to/my/client.key"
  }
}

These settings would just need to be used when constructing the transport fed to gzhttp here to do something like this:

func NewPrometheus(name, uri string, headers map[string]string, timeout time.Duration, concurrency, rl int, tlsConfig tls.Config) *Prometheus {
	transport := &http.Transport{TLSClientConfig: tlsConfig }
	prom := Prometheus{
		name:        name,
		unsafeURI:   uri,
		safeURI:     sanitizeURI(uri),
		headers:     headers,
		timeout:     timeout,
		client:      http.Client{Transport: gzhttp.Transport(transport)},
		locker:      newPartitionLocker((&sync.Mutex{})),
		rateLimiter: ratelimit.New(rl),
		concurrency: concurrency,
	}
	return &prom
}