# Agent Check: TCP RTT (go-metro)

## Overview

The TCP RTT check reports on roundtrip times between the host the agent is running on and any host it is communicating with. This check is passive and will only report RTT times for packets being sent and received from outside the check. The check itself will not send any packets.

This check is only shipped in the 64-bit DEB and RPM Datadog Agent v5 packages. The check is currently _not_ available with Datadog Agent v6.

## Setup

Follow the instructions below to install and configure this check for an Agent running on a host. For containerized environments, see the [Autodiscovery Integration Templates][1] for guidance on applying these instructions.

### Installation

The TCP RTT check-also known as [go-metro][2]-is packaged with the Agent, but requires additional system libraries. The check uses timestamps provided by the PCAP library to compute the time between any outgoing packet and the corresponding TCP acknowledgement. As such, PCAP must be installed and configured.

Debian-based systems should use one of the following:

```bash
sudo apt-get install libcap
sudo apt-get install libcap2-bin
```

Redhat-based systems should use one of these:

```bash
sudo yum install libcap
sudo yum install compat-libcap1
```

Finally, configure PCAP:

```bash
sudo setcap cap_net_raw+ep /opt/datadog-agent/bin/go-metro
```

### Configuration

Edit the `go-metro.yaml` file in your agent's `conf.d` directory. See the [sample go-metro.yaml][3] for all available configuration options.
The following is an example file that will show the TCP RTT times for app.datadoghq.com and 192.168.0.22:

```yaml
init_config:
  snaplen: 512
  idle_ttl: 300
  exp_ttl: 60
  statsd_ip: 127.0.0.1
  statsd_port: 8125
  log_to_file: true
  log_level: info
instances:
  - interface: eth0
    tags:
      - env:prod
    ips:
      - 45.33.125.153
    hosts:
      - app.datadoghq.com
```

*NOTE*: for go-metro to run unprivileged, you will have to set CAP_NET_RAW capabilities on the binary:
```
# Install required libraries
$ sudo apt-get install libcap  # debian
$ sudo apt-get install libcap2-bin  # debian alternative
$ sudo yum install libcap  # redhat
$ sudo yum install compat-libcap1  # redhat alternative

# Set capabilities
$ sudo setcap cap_net_raw+ep /opt/datadog-agent/bin/go-metro
```

Because of different package names for different distros, if the instructions above
don't work for you, please issue an `apt-cache search libcap` or `yum search libcap` and you
should get a shortlist of packages that might provide the binary. Feel free to reach out
should you require assistance.

Also, please note that go-metro logs to its own file - found in `/var/log/datadog/go-metro.log`.
Additionally, go-metro runs standalone so it will *NOT* currently appear on the Agent's info page.

Finally, because the go-metro binary is only bundled with the 64-bit RPM and DEB distributions of the
Datadog Agent, it is only available in those packaged versions (i.e. go-metro is currently
unavailable with the source install or the 32-bit packages).

### Validation

To validate that the check is running correctly, you should see `system.net.tcp.rtt` metrics showing in the Datadog interface. Also, if you [Run the Agent's `status` subcommand][4], you should see something similar to the following:

```text
● datadog-agent.service - "Datadog Agent"
    Loaded: loaded (/lib/...datadog-agent.service; enabled; vendor preset: enabled)
    Active: active (running) since Thu 2016-03-31 20:35:27 UTC; 42min ago
  Process: 10016 ExecStop=/opt/.../supervisorctl -c /etc/dd-....conf shutdown (code=exited, status=0/SUCCESS)
  Process: 10021 ExecStart=/opt/.../start_agent.sh (code=exited, status=0/SUCCESS)
  Main PID: 10025 (supervisord)
    CGroup: /system.slice/datadog-agent.service
            ├─10025 /opt/datadog-...python /opt/datadog-agent/bin/supervisord -c /etc/dd-agent/supervisor.conf
            ├─10043 /opt/datadog-...python /opt/datadog-agent/agent/dogstatsd.py --use-local-forwarder
            ├─10044 /opt/datadog-agent/bin/go-metro -cfg=/etc/dd-agent/conf.d/go-metro.yaml
            ├─10046 /opt/datadog-.../python /opt/datadog-agent/agent/ddagent.py
            └─10047 /opt/datadog-.../python /opt/datadog-agent/agent/agent.py foreground --use-local-forwarder
```

If the TCP RTT check has started you should see something similar to the go-metro line above.

**This is a passive check, so unless there are packets actively being sent to the hosts mentioned in the yaml file, the metrics are not reported.**

## Data Collected

### Metrics

See [metadata.csv][5] for a list of metrics provided by this check.

### Events

The Go-metro check does not include any events.

### Service Checks

The Go-metro check does not include any service checks.

## Troubleshooting

Need help? Contact [Datadog support][6].

[1]: https://docs.datadoghq.com/agent/kubernetes/integrations/
[2]: https://github.com/DataDog/go-metro
[3]: https://github.com/DataDog/integrations-core/blob/master/go-metro/conf.yaml.example
[4]: https://docs.datadoghq.com/agent/guide/agent-commands/#agent-status-and-information
[5]: https://github.com/DataDog/integrations-core/blob/master/go-metro/metadata.csv
[6]: https://docs.datadoghq.com/help/
