envelope-exec Command Line Utility

The envelope-exec command executes a user-provided command that will connect to a service running the M-Lab platform, behind the access envelope.

Simply, envelope-exec contacts the Locate API, to find a list of nearby healthy service names, opens a websocket connection to one of the access envelope URLs returned, and then executes a user-provided command.

The following describes the conventions the user-provided command should support.

Services Using the Access Envelope

Not all services on M-Lab use the access envelope. It is the users responsibility to determine if this is the case before using envelope-exec.

The envelope-exec command will provide the target service URL and service name in environment variables so that the user-provided command can target a specific service and machine. It is up to the user-provided command to include service-specific ports where required.

The envelope-exec command creates two environment variables:

• SERVICE_URL - the original websocket url to the access envelope.
• SERVICE_HOSTNAME - the target service hostname.

A service that uses the access envelope is wehe/replay.

go get github.com/m-lab/access/cmd/envelope-exec
# Show the variables available to user-provided commands.
envelope-exec bash -c "env"
# Run a replay using the $SERVICE_HOSTNAME provided the variables available to
# user-provided commands.
envelope-exec bash -c "python src/replay_client.py
  --pcap_folder=./replayTraces/Vimeo_12122018/
  --serverInstance=$SERVICE_HOSTNAME"