title: How to check specific tcp port availibility with blackbox_exporter?
body: <p>I want to check the availability of tcp port 1521 on the Oracle database server.</p>
  
  <p>but probe_success shows 0, although the port is available.
  Target incorrect?</p>
  
  <p>my config prometheus.</p>
  
  <pre><code>  - job_name: 'blackbox'
      metrics_path: /probe
      params:
        module: ['http_2xx', 'tcp_connect']  # Look for a HTTP 200 response.
      static_configs:
        - targets:
          - 172.27.1.8:1521 # Target to probe with http on port 1521.
      relabel_configs:
        - source_labels: [__address__]
          target_label: __param_target
        - source_labels: [__param_target]
          target_label: instance
        - target_label: __address__
          replacement: 172.27.1.54:9115  
  </code></pre>
  
  <p>blackbox.yml</p>
  
  <pre><code>modules:
    http_2xx:
      prober: http
    http_post_2xx:
      prober: http
      http:
        method: POST
    tcp_connect:
      prober: tcp
    pop3s_banner:
      prober: tcp
      tcp:
        query_response:
        - expect: "^+OK"
        tls: true
        tls_config:
          insecure_skip_verify: false
    ssh_banner:
      prober: tcp
      tcp:
        query_response:
        - expect: "^SSH-2.0-"
    irc_banner:
      prober: tcp
      tcp:
        query_response:
        - send: "NICK prober"
        - send: "USER prober prober prober :prober"
        - expect: "PING :([^ ]+)"
          send: "PONG ${1}"
        - expect: "^:[^ ]+ 001"
    icmp:
      prober: icmp
  </code></pre>