STAP-EXPORTER(8)

NAME
stap-exporter - systemtap-prometheus interoperation mechanism

SYNOPSIS

stap-exporter [ OPTIONS ]

DESCRIPTION

stap-exporter runs a set of systemtap scripts and relays their procfs outputs to remote HTTP clients on demand. This makes systemtap scripts directly usable as individual prometheus exporters. This is assisted by a set of macros provided in the prometheus.stpm tapset file.

OPTIONS

The stap-exporter program supports the following options.

-p --port PORT
    Listen to the specified TCP port for HTTP requests. Port 9900 is used by default.

-k --keepalive KEEPALIVE
    Scripts that run longer than KEEPALIVE seconds beyond the last request are shut down. There is no timeout by default, so once started, scripts are kept running.

-s --scripts SCRIPTS
    Search the directory SCRIPTS for *.stp files to be exposed. The default is given in the stappaths.7 man page.

-h --help
    Print help message.

OPERATION

Upon startup, stap-exporter searches the directory specified by the -s directory for files named *.stp. The name of each file becomes available as a URL component for subsequent GET HTTP requests. For example, when an HTTP client asks for /foo.stp, and the foo.stp script (executable / shell-script) was known, then it is spawned with additional stap options to set a module name. This predictable module name makes it possible for stap-exporter to transcribe a procfs file from that running script to HTTP clients.

After a configurable period of disuse (-k or --keepalive option), a systemtap script is terminated. It will be restarted again if a client requests.

All files whose name includes the substring autostart are started immediately (and restarted if they stop), rather than on-demand. These are excluded from keepalive considerations. Scripts that may be too slow to start or wish to report long-term statistics are candidates for this treatment.

EXAMPLE

Suppose that example.stp contains the following script. It counts read syscalls on a per-thread & per-cpu basis.

global arr%

probe syscall.read {
    arr[tid(), cpu()]++ }

probe prometheus {
    @prometheus_dump_array2(arr, "count", "tid", "cpu") }

The prometheus_dump_array macros are used to produce metrics from an array. Systemtap provides a prometheus_dump_arrayN macro for all N from 1 to 8. The first argument of the macros represents an array with N-element keys. The second argument represents the name of the metric. The remaining N arguments represent the names of the metric's labels.

One may launch stap-exporter as root, or equivalent stapdev privileges, then after a brief delay, use any web client to fetch data:

# stap-exporter -p 9999 -k 60 -c . &

$ curl http://localhost:9999/example.stp Refresh page to access metrics. [...]

$ curl http://localhost:9999/example.stp count{tid="12614",cpu="0"} 9 count{tid="12170",cpu="3"} 107 count{tid="1802",cpu="0"} 33687 count{tid="12617",cpu="1"} 99 [...]

The same URL may be added to a Prometheus server's scrape_config section, or a Performance Co-Pilot pmdaprometheus config.d directory, to collect this data into a monitoring system.

SAFETY AND SECURITY

The stap-exporter server does not enforce any particular security mechanisms. Therefore, deployment in an untrusted environment needs to consider:

script selection
    Since systemtap scripts are run under the privileges of the stap-exporter process (probably root), the system administrator must select only safe & robust scripts. Check the scripts installed by default before activating the service. Scripts cannot take input from the web clients.

TCP/IP firewalling
    Since stap-exporter exposes the selected TCP/HTTP port to all interfaces on the host, it may be necessary to add a firewall. It is unlikely to be appropriate to expose such a service to an untrusted network.

HTTP filtering
    Since stap-exporter exposes the configured systemtap scripts to all HTTP clients without authentication, it may be necessary to protect it from abuse even on mostly trusted networks. An HTTP proxy may be used to impose URL- or client- or usage- or authentication-dependent filters.

HTTPS
    Since stap-exporter speaks only plain HTTP, an HTTP proxy may be used to support HTTPS secure protocols.

SEE ALSO
stap(1), stapprobes(3stap), stappaths(7) tapset::prometheus(7)

BUGS
Use the Bugzilla link of the project web page or our mailing list. http://sourceware.org/systemtap/, <systemtap@sourceware.org>.

error::reporting(7stap), https://sourceware.org/systemtap/wiki/HowToReportBugs