Add documentation on how to ingest resticprofile stats into telegraf (#…

…366)

* Add information on how to push backup stats to Telegraf

* Fix the directory name

* Nitpicks addressed.

* Update README.md for telegraf 1.31

contrib/telegraf/README.md

@@ -0,0 +1,32 @@
+# backup stats in InfluxDB via Telegraf
+
+Telegraf can ingest stats produced by resticprofile in two different ways:
+
+1. Configure [http_listener_v2](https://github.com/influxdata/telegraf/tree/master/plugins/inputs/http_listener_v2) expecting Prometheus data, have resticprofile push to it via `prometheus-push`. You need telegraf version [1.31 or higher](https://github.com/influxdata/telegraf/issues/15453). You also need to explicitly configure urls on telegraf side, like so:
+
+```toml
+[[inputs.http_listener_v2]]
+  paths = [
+    "/metrics/job/profilename.backup",
+    "/metrics/job/anotherprofile.backup"
+  ]
+  service_address = ":9999"
+  http_success_code = 200
+  data_format = "prometheus"
+```
+
+2. Configure telegraf to parse resticprofile's JSON status file. This works only if telegraf can access the file that resticprofile produces. It can also break if the status file format changes.
+
+```toml
+[[inputs.file]]
+  files = ["/var/cache/restic/status.json"]
+  data_format = "json_v2"
+  [[inputs.file.json_v2]]
+    measurement_name = "restic"
+    [[inputs.file.json_v2.object]]
+      path = "{backup_profile:profiles.@keys,stats:profiles.@values}.@group"
+      disable_prepend_keys = true
+      timestamp_key = "stats_backup_time"
+      timestamp_format = "rfc3339nano"
+      tags = ["backup_profile"]
+```