Project: Netdata (Observability and Analysis / Observability)
File: go_applications_expvar.md

<!--startmeta customediturl: "https://github.com/netdata/netdata/edit/master/src/collectors/python.d.plugin/go_expvar/README.md" metayaml: "https://github.com/netdata/netdata/edit/master/src/collectors/python.d.plugin/goexpvar/metadata.yaml" sidebar_label: "Go applications (EXPVAR)" learn_status: "Published" learnrelpath: "Collecting Metrics/APM" most_popular: False message: "DO NOT EDIT THIS FILE DIRECTLY, IT IS GENERATED BY THE COLLECTOR'S metadata.yaml FILE" endmeta--> <img src="https://netdata.cloud/img/go.png" width="150"/> Plugin: python.d.plugin Module: go_expvar <img src="https://img.shields.io/badge/maintained%20by-Netdata-%2300ab44" /> This collector monitors Go applications that expose their metrics with the use of the `expvar` package from the Go standard library. It produces charts for Go runtime memory statistics and optionally any number of custom charts. It connects via http to gather the metrics exposed via the `expvar` package. This collector is supported on all platforms. This collector supports collecting metrics from multiple instances of this integration, including remote instances. This integration doesn't support auto-detection. The default configuration for this integration does not impose any limits on data collection. The default configuration for this integration is not expected to impose a significant performance impact on the system. Metrics grouped by scope. The scope defines the instance that the metric belongs to. An instance is uniquely identified by a set of labels. These metrics refer to the entire monitored application. This scope has no labels. Metrics: | Metric | Dimensions | Unit | |:|:-|:-| | expvar.memstats.heap | alloc, inuse | KiB | | expvar.memstats.stack | inuse | KiB | | expvar.memstats.mspan | inuse | KiB | | expvar.memstats.mcache | inuse | KiB | | expvar.memstats.live_objects | live | objects | | expvar.memstats.sys | sys | KiB | | expvar.memstats.gc_pauses | avg | ns | There are no alerts configured by default for this integration. The `go_expvar` collector is disabled by default. To enable it, use `edit-config` from the Netdata , which is typically at `/etc/netdata`, to edit the `python.d.conf` file. ```bash cd /etc/netdata # Replace this path with your Netdata config directory, if different sudo ./edit-config python.d.conf ``` Change the value of the `go_expvar` setting to `yes`. Save the file and restart the Netdata Agent with `sudo systemctl restart netdata`, or the for your system. The `expvar` package exposes metrics over HTTP and is very easy to use. Consider this minimal sample below: ```go package main import ( _ "expvar" "net/http" ) func main() { http.ListenAndServe("127.0.0.1:8080", nil) } ``` When imported this way, the `expvar` package registers a HTTP handler at `/debug/vars` that exposes Go runtime's memory statistics in JSON format. You can inspect the output by opening the URL in your browser (or by using `wget` or `curl`). Sample output: ```json { "cmdline": ["./expvar-demo-binary"], "memstats": {"Alloc":630856,"TotalAlloc":630856,"Sys":3346432,"Lookups":27, <omitted for brevity>} } ``` You can of course expose and monitor your own variables as

Here is a sample Go application that exposes a few custom variables: ```go package main import ( "expvar" "net/http" "runtime" "time" ) func main() { tick := time.NewTicker(1 * time.Second) num_go := expvar.NewInt("runtime.goroutines") counters := expvar.NewMap("counters") counters.Set("cnt1", new(expvar.Int)) counters.Set("cnt2", new(expvar.Float)) go http.ListenAndServe(":8080", nil) for { select { case <- tick.C: num_go.Set(int64(runtime.NumGoroutine())) counters.Add("cnt1", 1) counters.AddFloat("cnt2", 1.452) } } } ``` Apart from the runtime memory stats, this application publishes two counters and the number of currently running Goroutines and updates these stats every second. The configuration file name for this integration is `python.d/go_expvar.conf`. You can edit the configuration file using the `edit-config` script from the Netdata . ```bash cd /etc/netdata 2>/dev/null || cd /opt/netdata/etc/netdata sudo ./edit-config python.d/go_expvar.conf ``` There are 2 sections: Global variables One or more JOBS that can define multiple different instances to monitor. The following options can be defined globally: priority, penalty, autodetectionretry, updateevery, but can also be defined per JOB to override the global values. Additionally, the following collapsed table contains all the options that can be configured inside a JOB definition. Every configuration JOB starts with a `job_name` value which will appear in the dashboard, unless a `name` parameter is specified. Each JOB can be used to monitor a different Go application. <details><summary>Config options</summary> | Name | Description | Default | Required | |:-|:--|:-|:--:| | update_every | Sets the default data collection frequency. | 5 | no | | priority | Controls the order of charts at the netdata dashboard. | 60000 | no | | autodetection_retry | Sets the job re-check interval in seconds. | 0 | no | | penalty | Indicates whether to apply penalty to update_every in case of failures. | yes | no | | name | Job name. This value will overwrite the `job_name` value. JOBS with the same name are mutually exclusive. Only one of them will be allowed running at any time. This allows autodetection to try several alternatives and pick the one that works. | | no | | url | the URL and port of the expvar endpoint. Please include the whole path of the endpoint, as the expvar handler can be installed in a non-standard location. | | yes | | user | If the URL is password protected, this is the username to use. | | no | | pass | If the URL is password protected, this is the password to use. | | no | | collect_memstats | Enables charts for Go runtime's memory statistics. | | no | | extra_charts | Defines extra data/charts to monitor, please see the example below. | | no | </details> The example below sets a configuration for a Go application, called

Besides the `memstats`, the application also exposes two counters and the number of currently running Goroutines and updates these stats every second. The `goexpvar` collector can monitor these as well with the use of the `extracharts` configuration variable. The `extra_charts` variable is a YaML list of Netdata chart definitions. Each chart definition has the following keys: ``` id: Netdata chart ID options: a key-value mapping of chart options lines: a list of line definitions ``` Note: please do not use dots in the chart or line ID field. See for explanation. Please see these two links to the official Netdata documentation for more information about the values: Line definitions Each chart can define multiple lines (dimensions). A line definition is a key-value mapping of line options. Each line can have the following options: ``` expvar_key: the name of the expvar as present in the JSON output of /debug/vars endpoint expvar_type: value type; supported are "float" or "int" id: the id of this line/dimension in Netdata name: '' algorithm: absolute multiplier: 1 divisor: 100 if expvartype == float, 1 if expvartype == int hidden: False ``` Please see the following link for more information about the options and their default values: Apart from top-level expvars, this plugin can also parse expvars stored in a multi-level map; All dicts in the resulting JSON document are then flattened to one level. Expvar names are joined together with '.' when flattening. Example: ``` { "counters": {"cnt1": 1042, "cnt2": 1512.9839999999983}, "runtime.goroutines": 5 } ``` In the above case, the exported variables will be available under `runtime.goroutines`, `counters.cnt1` and `counters.cnt2` expvar_keys. If the flattening results in a key collision, the first defined key wins and all subsequent keys with the same name are ignored. ```yaml app1: name : 'app1' url : 'http://127.0.0.1:8080/debug/vars' collect_memstats: true extra_charts: id: "runtime_goroutines" options: name: num_goroutines title: "runtime: number of goroutines" units: goroutines family: runtime context: expvar.runtime.goroutines chart_type: line lines: {expvarkey: 'runtime.goroutines', expvartype: int, id: runtime_goroutines} id: "foo_counters" options: name: counters title: "some random counters" units: awesomeness family: counters context: expvar.foo.counters chart_type: line lines: {expvarkey: 'counters.cnt1', expvartype: int, id: counters_cnt1} {expvarkey: 'counters.cnt2', expvartype: float, id: counters_cnt2} ``` To troubleshoot issues with the `go_expvar` collector, run the `python.d.plugin` with the debug option enabled. The output should give you clues as to why the collector isn't working. Navigate to the `plugins.d` directory, usually at `/usr/libexec/netdata/plugins.d/`. If that's not the case on your system, open `netdata.conf` and look for the `plugins` setting under `[directories]`. ```bash cd /usr/libexec/netdata/plugins.d/ ``` Switch to the `netdata` user. ```bash sudo -u netdata -s ``` Run the `python.d.plugin` to debug the collector: ```bash ./python.d.plugin go_expvar debug trace ```