big-graf: use grafterm to display a single full-terminal Prometheus graph

big-graf

#!/bin/sh -eu
write() {
    _TARGET=$1

    _ADDRESS="${BIG_GRAF_PROMETHEUS_ADDRESS:-"http://localhost:9090"}"
    _TITLE="${GRAPH_TITLE:-""}"
    _QUERY="$(echo "${GRAPH_QUERY:-"up"}" | sed 's,",\\",g')"
    _LEGEND="${GRAPH_LEGEND:-"{{ .instance }}"}"
    _UNIT="${GRAPH_UNIT:-""}"
    _DECIMALS="${GRAPH_DECIMALS:-0}"

    cat << EOT > "$_TARGET"
{
    "version": "v1",
    "datasources": {
        "ds": {
            "prometheus": {
                "address": "${_ADDRESS}"
            }
        }
    },
    "dashboard": {
        "widgets": [
            {
                "title": "${_TITLE}",
                "gridPos": { "w": 100 },
                "graph": {
                    "queries": [
                        {
                            "datasourceID": "ds",
                            "expr": "${_QUERY}",
                            "legend": "${_LEGEND}"
                        }
                    ],
                    "visualization": {
                        "yAxis": { "unit": "${_UNIT}", "decimals": ${_DECIMALS} }
                    }
                }
            }
        ]
    }
}
EOT
}

help() {
    cat << EOH
$0: generate a grafterm configuration and invoke grafterm with it

It reads the following environment variables:

BIG_GRAF_PROMETHEUS_ADDRESS
    The Prometheus instance to query (default: http://localhost:9090)
GRAPH_TITLE
    The title of the graph (default: no title)
GRAPH_QUERY
    The query to execute against the Prometheus instance (default: "up")
GRAPH_LEGEND
    The legend to use for the graph, uses Go's templating language against
    the query result (default: "{{ .instance }}")
GRAPH_UNIT
    The unit to use for the Y-axis of the graph, see grafterm's documentation
    for the options (default: no units)
GRAPH_DECIMALS
    The number of decimals for the Y-axis of the graph (default: 0)

Any arguments are passed through to grafterm itself: see 'grafterm --help'
for available options, including those related to query time range.
EOH
}

main() {
    tmpfile="$(mktemp)"
    cleanup() {
        [ -e "$tmpfile" ] && rm "$tmpfile"
    }
    trap cleanup EXIT

    write "$tmpfile"
    grafterm -c "$tmpfile" $@
}

case "$0 $@" in
    *" -h"*|*" --help"*)
        help
        exit 0
        ;;
esac

main $@