Add support for textfile collector.

Author: brian-brazil

README.md

@@ -110,7 +110,11 @@ c.labels('post', '/submit').inc()
 
 ## Exporting
 
-Metrics are exposed over HTTP, to be read by the Prometheus server. For example:
+There are several options for exporting metrics.
+
+## HTTP handler
+
+Metrics are usuall exposed over HTTP, to be read by the Prometheus server. For example:
 
 ```python
 from prometheus_client import MetricsHandler
@@ -121,3 +125,22 @@ httpd.serve_forever()
 ```
 
 Visit [http://localhost:8000/](http://localhost:8000/) to view the metrics.
+
+## Node exporter textfile collector
+
+The [textfile collector](https://github.com/prometheus/node_exporter#textfile-collector)
+allows machine-level statistics to be exported out via the Node exporter.
+
+This is useful for monitoring cronjobs, or for writing cronjobs to expose metrics
+about your system that the Node exporter does not support or would not make sense
+to perform at every scrape (for example, anything involving subprocesses).
+
+```python
+from prometheus_client import CollectorRegistry,Gauge,write_to_textfile
+registry = CollectorRegistry()
+g = Gauge('raid_status', '1 if raid array is okay', registry=registry)
+g.set(1)
+write_to_textfile('/configured/textfile/path/raid.prom', registry)
+```
+
+A separate registry is used, as the default registry may contain other metrics.

prometheus_client/__init__.py

@@ -2,7 +2,9 @@
 
 import copy
 import re
+import os
 import time
+import threading
 from contextlib import contextmanager
 from BaseHTTPServer import BaseHTTPRequestHandler
 from functools import wraps
@@ -318,6 +320,17 @@ def do_GET(self):
     self.end_headers()
     self.wfile.write(generate_latest(REGISTRY))
 
+def write_to_textfile(path, registry):
+  '''Write metrics to the given path.
+
+  This is intended for use with the Node exporter textfile collector.
+  The path must end in .prom for the textfile collector to process it.'''
+  tmppath = '%s.%s.%s' % (path, os.getpid(), threading.current_thread().ident)
+  with open(tmppath, 'wb') as f:
+    f.write(generate_latest(registry))
+  # rename(2) is atomic.
+  os.rename(tmppath, path)
+
 
 if __name__ == '__main__':
   c = Counter('cc', 'A counter')

setup.py

@@ -10,7 +10,7 @@ def read(fname):
 
 setup(
     name = "prometheus_client",
-    version = "0.0.2",
+    version = "0.0.3",
     author = "Brian Brazil",
     author_email = "[email protected]",
     description = ("Python client for the Prometheus monitoring system."),