What is it?

The tracereplay tool can save runsc trace sessions to a file, and later replay the same sequence of messages. This can be used to run tests that rely on the messages without the need to setup runsc, configure trace sessions, and run specific workloads.

How to use it?

The tracereplay save command starts a server that listens to new connections from runsc and creates a trace file for each runsc instance that connects to it. The command below starts a server on listening on /tmp/gvisor_events.sock and writes trace files to /tmp/trace directory:

$ tracereplay save --endpoint=/tmp/gvisor_events.sock --out=/tmp/trace

When you execute runsc configured with a trace session using the remote sink connecting to /tmp/gvisor_events.sock, all messages will be saved to a file under /tmp/trace. For example, if you run the following commands, runsc will connect to the server above and all trace points triggered by the workload will be stored in the save file:

$ cat > /tmp/pod_init.json <<EOL
{
  "trace_session": {
    "name": "Default",
    "points": [
      {
        "name": "container/start"
      }
    ],
    "sinks": [
      {
        "name": "remote",
        "config": {
          "endpoint": "/tmp/gvisor_events.sock"
        }
      }
    ]
  }
}
EOL
$ runsc --rootless --network=none --pod-init-config=/tmp/pod_init.json do /bin/true

You should see the following output from tracereplay save:

New client connected, writing to: "/tmp/trace/client-0001"
Closing client, wrote 1 messages to "/tmp/trace/client-0001"

You can then use the tracereplay replay command to replay the exact same messages anytime and as many times as you want. Here is an example using the file created above:

$ tracereplay replay --endpoint=/tmp/gvisor_events.sock --in=/tmp/trace/client-0001
Handshake completed
Replaying message: 1
Done

If you want to see the messages that are stored in the file, you can setup the example server provided in examples/seccheck:server_cc and replay the save file using the same command above. Here is the output you would get:

$ bazel run examples/seccheck:server_cc
Socket address /tmp/gvisor_events.sock
Connection accepted
Start => id:     "runsc-865139" cwd: "/home/fvoznika" args: "/bin/true"
Connection closed