Merge pull request #12 from signal-ai/allow-customising-default-sd

Makefile

@@ -5,4 +5,4 @@ format:
 .PHONY: dev-start
 dev-start:
 	@mkdir -p ./targets
-	poetry run python discoverecs.py --directory $$PWD/targets
+	poetry run python discoverecs.py --directory $$PWD/targets --default-scrape-interval-prefix default

README.md

@@ -60,8 +60,7 @@ The output directory is then `/opt/prometheus-ecs` defined in your Prometheus co
         regex: (.+)
 ```
 
-You can also specify a discovery interval with `--interval` (in seconds). Default is 60s. We also provide caching to minimize hitting query
-rate limits with the AWS ECS API. `discoverecs.py` runs in a loop until interrupted and will output target information to stdout.
+You can also specify a discovery interval with `--interval` (in seconds). The default is `60s`. We also provide caching to minimize hitting query rate limits with the AWS ECS API. `discoverecs.py` runs in a loop until interrupted and will output target information to stdout.
 
 To make your application discoverable by Prometheus, you need to set the following environment variable in your task definition:
 
@@ -72,9 +71,11 @@ To make your application discoverable by Prometheus, you need to set the followi
 Metric path and scrape interval is supported via `PROMETHEUS_ENDPOINT`:
 
 ```text
-"interval:/metric_path,..."
+"[interval:]<metric_path>,..."
 ```
 
+where `interval` is optional.
+
 Examples:
 
 ```text
@@ -91,7 +92,23 @@ Under ECS task definition (`task.json`):
 
 Available scrape intervals: `15s`, `30s`, `1m`, `5m`.
 
-The default metric path is `/metrics`. The default scrape interval is `1m`.
+The default metric path is `/metrics`.
+
+### Default scrape interval
+
+The default scrape interval is `1m` when no interval is specified in the `PROMETHEUS_ENDPOINT` variable.
+
+This can be customised using the option `--default-scrape-interval-prefix`. This can be any string which will result in the targets being output to `/opt/prometheus-ecs/<default_scrape_interval>-tasks.json` being written.
+
+e.g. if `default` is used:
+
+```shell
+--default-scrape-interval-prefix default
+```
+
+then `/opt/prometheus-ecs/default-tasks.json` will be written. This can be useful to allow configuration of a default scrape interval in your Prometheus config, rather than needing to update the config and then redeploying this discovery service.
+
+### Configuration yaml
 
 The following Prometheus configuration should be used to support all available intervals:
 

discoverecs.py

@@ -341,11 +341,11 @@ def extract_path_interval(env_variable):
                 if re.search("(15s|30s|1m|5m)", pi[0]):
                     path_interval[pi[1]] = pi[0]
                 else:
-                    path_interval[pi[1]] = "1m"
+                    path_interval[pi[1]] = None
             else:
-                path_interval[lst] = "1m"
+                path_interval[lst] = None
     else:
-        path_interval["/metrics"] = "1m"
+        path_interval["/metrics"] = None
     return path_interval
 
 
@@ -457,14 +457,15 @@ def task_info_to_targets(task_info):
 
 
 class Main:
-    def __init__(self, directory, interval):
+    def __init__(self, directory, interval, default_scrape_interval_prefix):
         self.directory = directory
         self.interval = interval
+        self.default_scrape_interval_prefix = default_scrape_interval_prefix
         self.discoverer = TaskInfoDiscoverer()
 
     def write_jobs(self, jobs):
-        for i, j in jobs.items():
-            file_name = self.directory + "/" + i + "-tasks.json"
+        for prefix, j in jobs.items():
+            file_name = self.directory + "/" + prefix + "-tasks.json"
             tmp_file_name = file_name + ".tmp"
             with open(tmp_file_name, "w") as f:
                 f.write(json.dumps(j, indent=4))
@@ -511,7 +512,7 @@ def discover_tasks(self):
                 }
                 if labels:
                     job["labels"].update(labels)
-                jobs[interval].append(job)
+                jobs[interval or self.default_scrape_interval_prefix].append(job)
                 log(job)
         self.write_jobs(jobs)
 
@@ -525,15 +526,20 @@ def main():
     arg_parser = argparse.ArgumentParser()
     arg_parser.add_argument("--directory", required=True)
     arg_parser.add_argument("--interval", default=60)
+    arg_parser.add_argument("--default-scrape-interval-prefix", default="1m")
     args = arg_parser.parse_args()
     log(
-        "Starting. Directory: "
-        + args.directory
-        + ". Interval: "
-        + str(args.interval)
-        + "s."
+        'Starting...\nDirectory: "{}"\nRefresh interval: "{}s"\nDefault scrape interval prefix: "{}"\n'.format(
+            args.directory,
+            str(args.interval),
+            args.default_scrape_interval_prefix,
+        )
     )
-    Main(args.directory, float(args.interval)).loop()
+    Main(
+        directory=args.directory,
+        interval=float(args.interval),
+        default_scrape_interval_prefix=args.default_scrape_interval_prefix,
+    ).loop()
 
 
 if __name__ == "__main__":