General Tips

There are several approaches you can take to monitoring with Stylus. This section covers general best practices and tips for writing effective monitor scripts.

STYLUS_MONITOR_ID

The STYLUS_MONITOR_ID environment variable is set by Stylus to the monitor's ID when running a monitor script. This allows you to write monitor scripts that can be re-used across multiple monitors.

#!/bin/bash
set -xeuf -o pipefail
# Check the health of a service running on the monitor
curl --fail http://$STYLUS_MONITOR_ID:8080/health | jq --raw-output '.status'

Safe Scripting

Because monitor scripts may have a large number of moving parts, consider using safe shell scripting techniques to ensure that any failure of any kind will return an error code.

In addition set -x can be useful to print all commands that run as part of a monitor script. These are available in the logging endpoints and will show you the expansion of environment variables.

#!/bin/bash
set -xeuf -o pipefail

Script-relative Paths

The dirname command can be used to get the directory of the script that is running. This can be useful to locate configuration files or other resources that are needed by the script, which allows you to run the script from any directory outside of Stylus.

#!/bin/bash
set -xeuf -o pipefail
DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"

CONFIG_FILE=$DIR/config.yaml

Testing Your Configurations

As monitor scripts using metadata can be somewhat tricky to get right, Stylus includes a test command-line argument to allow you to develop your test script in a slightly more interactive manner.

The output from stylus test will include the test script's stdout and stderr streams, as well as the parsed monitor state as JSON, and the final rendered CSS.