Update README

README.md

@@ -1,11 +1,33 @@
 # huntflow-base-metrics
 Base definitions for metrics collection via prometheus client library.
-Intended to be used in Huntflow fastapi-based services: ready-to use collectors to measure HTTP requests and responses.
-Also provides universal decorator to observe timings of custom methods/functions.
+Intended to be used in Huntflow fastapi-based services:
+* ready-to use collectors to measure HTTP requests and responses.
+* decorator to observe timings of custom methods/functions.
+* builtin support for common lables across all collectors
 
-# How to use
+# Installation
 
-## How to collect metrics for FastAPI requests
+TODO
+
+# Usage
+
+## Common labels and methods
+
+The package provides two labels which should be set for every metric:
+
+* `service` - name for your service
+* `pod` - instance of your service (supposed to be k8s pod name)
+
+You don't need to set those labels manually. The labels are handled implicitly by the package public
+methods.
+
+For FastAPI metrics you don't need to deal with labels at all.
+
+For another metrics use `register_metric` method. It will accept a custom list of labels and create
+a collector with your labels + common labels. To get labelled metric instance (registered with `register_metric`) use
+`apply_labels` method.
+
+## Collect FastAPI requests metrics
 
 ```python
 from contextlib import asynccontextmanager
@@ -53,7 +75,124 @@ def create_app()
     )
     add_middleware(app)
     return app
+```
+
+### FastAPI metrics
+
+#### requests_total
+
+Incremental counter for total number of requests
+
+**Type** Counter
+
+**Labels**
+
+* `service`
+* `pod`
+* `method` - HTTP method like `GET`, `POST`
+* `template_path` - path provided as a route
+
+#### responses_total
+
+Incremental counter for total number of responses
+
+**Type** Counter
+
+**Labels**
+
+* `service`
+* `pod`
+* `method` - HTTP method like `GET`, `POST`
+* `template_path` - path provided as a route
+* `status_code` - HTTP status code return by response (200, 404, 500, etc)
+
+
+#### requests_processing_time_seconds
+
+Historgam collects latency (request processing time) for requests
+
+**Type** Histogram
+
+**Labels**
+
+* `service`
+* `pod`
+* `method` - HTTP method like `GET`, `POST`
+* `template_path` - path provided as a route
+* `le` - bucket in histogram (builtin label in Histogram collector)
+
+
+#### requests_in_progress
+
+Current number of in-progress requests 
+
+**Type** Gauge
+
+**Labels**
+
+* `service`
+* `pod`
+* `method` - HTTP method like `GET`, `POST`
+* `template_path` - path provided as a route
+
+## Observe timing for custom methods
+
+To collect metrics for some method (not FastAPI handlers) use `observe_metrics` decorator.
+It can be applied to regular and for async functions/methods.
+It accepts two required parameters:
+
+* method - string to identify measured method
+* metric_timings - Histogram instance to collect timing
+
+Third optional parameter is `metric_inprogress` (instance of Gauge colector).
+Provide it if you need to collect in-progress operations for the observing method.
+
+To create Histogram object useful for `observe_metrics`, call `register_method_observe_histogram`
+function. It accepts two parameters:
+* name - unique metric name (first argument for Histogram constructor)
+* description - metric description
+
+**Labels provided by metric_timings**
+
+* `service`
+* `pod`
+* `method` - method name passed to observe_metrics decorator
+* `le` - bucket name (built-in label of Histogram collector)
+
+Usage example
+
+```python
+from huntflow_base_metrics import (
+    register_method_observe_histogram,
+    observe_metrics,
+)
+
+
+METHOD_HISTOGRAM = register_method_observe_histogram(
+    "process_method_timing",
+    "Timings for processing logic",
+)
+
+
+@observe_metrics("select_data", METHOD_HISTOGRAM)
+async def select_data(filters) -> List[Dict]:
+    data = [convert_item(record for record in await repo.select(*filters)]
+    return data
+
+
+@observe_metrics("convert_item", METHOD_HISTOGRAM)
+def convert_item(record: Dict) -> RecordDTO:
+    return RecrodDTO(**record)
+
+
+@observe_metrics("calculate_stats", METHOD_HISTOGRAM)
+async def calculate_stats(filters) -> StatsDTO:
+    data = await select_data(filters)
+    stats = aggregate(data)
+    return stats
+
 
 ```
 
+
 # TODO: another use-cases and development notes