TCP RTT check

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 Stackstate Agent packages.

Setup

Installation

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:

$ sudo apt-get install libcap
$ sudo apt-get install libcap2-bin

Redhat-based systems should use one of these:

$ sudo yum install libcap
$ sudo yum install compat-libcap1

Finally, configure PCAP:

$ sudo setcap cap_net_raw+ep /opt/stackstate-agent/bin/go-metro

Configuration

Edit the go-metro.yaml file in your agent’s conf.d directory. The following is an example file that will show the TCP RTT times for stackstate.com and 192.168.0.22:

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.stackstate.com

Validation

To validate that the check is running correctly, you should see system.net.tcp.rtt metrics showing in the Stackstate interface. Also, if you run sudo /etc/init.d/stackstate-agent status, you should see something similar to the following:

● stackstate-agent.service - "Stackstate Agent"
   Loaded: loaded (/lib/...stackstate-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/sts-....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/stackstate-agent.service
           ├─10025 /opt/stackstate-...python /opt/stackstate-agent/bin/supervisord -c /etc/sts-agent/supervisor.conf
           ├─10043 /opt/stackstate-...python /opt/stackstate-agent/agent/stsstatsd.py --use-local-forwarder
           ├─10044 /opt/stackstate-agent/bin/go-metro -cfg=/etc/sts-agent/conf.d/go-metro.yaml
           ├─10046 /opt/stackstate-.../python /opt/stackstate-agent/agent/ddagent.py
           └─10047 /opt/stackstate-.../python /opt/stackstate-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 will not be reported.

Data Colleted

Metrics

system.net.tcp.rtt
(gauge)
The TCP round trip time.
shown as millisecond
system.net.tcp.rtt.avg
(gauge)
The average TCP round trip time as typically computed by the TCP stack.
shown as millisecond
system.net.tcp.rtt.jitter
(gauge)
The TCP round trip time jitter.
shown as millisecond