metrics.md

Firecracker Metrics Configuration

For the metrics capability, Firecracker uses a single Metrics system. This system can be configured by sending a PUT API Request to the /metrics path.

Prerequisites

In order to configure the Metrics, first you have to create the resource that will be used for storing the metrics:

# Create the required named pipe:
mkfifo metrics.fifo

# The Metrics system also works with usual files:
touch metrics.file

Configuring the system

You can configure the Metrics system by sending the following API command:

curl --unix-socket /tmp/firecracker.socket -i \
    -X PUT "http://localhost/metrics" \
    -H "accept: application/json" \
    -H "Content-Type: application/json" \
    -d "{
             \"metrics_path\": \"metrics.fifo\"
    }"

Details about this configuration can be found in the swagger definition.

The metrics are written to the metrics_path in JSON format.

Flushing the metrics

The metrics get flushed in two ways:

• without user intervention every 60 seconds;

• upon user demand, by issuing a FlushMetrics request. You can find how to use this request in the actions API.

If the path provided is a named pipe, you can use the script below to read from it:

metrics=metrics.fifo

while true
do
    if read line <$metrics; then
        echo $line
    fi
done

echo "Reader exiting"

Otherwise, if the path points to a normal file, you can simply do:

cat metrics.file