Lab 12, task 1

Author: kolayne

app_python/.gitignore

@@ -174,3 +174,6 @@ poetry.toml
 pyrightconfig.json
 
 # End of https://www.toptal.com/developers/gitignore/api/python
+
+
+/persistent

app_python/Dockerfile

@@ -7,6 +7,8 @@ COPY requirements.txt /app/
 COPY moscow_time/ /app/moscow_time
 # Note: keeping the project files owned by root so
 # the web server has less privileges over them
+RUN ["mkdir", "--mode", "777", "/app/persistent"]
+VOLUME /app/persistent
 USER flask:flask
 RUN ["pip", "install", "--user", "-r", "requirements.txt"]
 CMD ["python", "-m", "moscow_time"]

app_python/README.md

@@ -54,6 +54,9 @@ docker run --rm -d -p 5000 kolay0ne/app_py
 
 Replace `kolay0ne/app_py` with your image/tag name if you built it manually.
 
+One may want to mount a volume or a bind-mount at `/app/persistent`, which acts
+as a persistent storage for the visits counter of the web app.
+
 ## Unit Tests
 
 To run unit tests:

app_python/moscow_time/__init__.py

@@ -1,11 +1,13 @@
 import datetime
+from os import makedirs
 from time import monotonic
 
-from flask import Flask, request, Response
+from flask import Flask, request, Response, send_from_directory
 import requests
 import prometheus_client
 
 from .cache import cache_for
+from .visits import increment_on_call
 
 
 app = Flask(__name__)
@@ -42,12 +44,32 @@ def get_time():
     return dt.time()
 
 
+VISITS_FILENAME = 'persistent/visits.bin'
+
+# Create it on start
+try:
+    basename_at = VISITS_FILENAME.rindex('/')
+except ValueError:
+    pass
+else:
+    makedirs(VISITS_FILENAME[:basename_at], exist_ok=True)
+open(VISITS_FILENAME, 'a+').close()  # The `a+` mode ensures we have write perm
+
+
 @app.route('/')
+@increment_on_call(VISITS_FILENAME)
 def index():
     time = get_time()
     return f"In MSK it's {time.hour}:{time.minute}:{time.second}. " \
         "Have you brushed your teeth today yet?"
 
 @app.route('/metrics')
+@increment_on_call(VISITS_FILENAME)
 def prometheus_metrics():
     return Response(prometheus_client.generate_latest(), mimetype='text/plain')
+
+@app.route('/visits')
+@increment_on_call(VISITS_FILENAME)
+def visits():
+    with open(VISITS_FILENAME, 'rb') as f:
+        return str(int.from_bytes(f.read(), byteorder='little'))

app_python/moscow_time/visits.py

@@ -0,0 +1,28 @@
+import fcntl
+from functools import wraps
+from threading import Lock
+from typing import Callable
+
+
+def increment(filename: str) -> None:
+    with open(filename, 'rb+') as f:
+        try:
+            fcntl.flock(f.fileno(), fcntl.LOCK_EX)
+            cur = int.from_bytes(f.read(), byteorder='little')
+            f.seek(0)
+            cur += 1
+            f.write(cur.to_bytes(byteorder='little', length=(cur.bit_length() // 8 + 1)))
+            f.truncate()  # Not necessary, as larger numbers take more bytes
+        finally:
+            # Note: will be unlocked anyway when the file is closed
+            fcntl.flock(f.fileno(), fcntl.LOCK_UN)
+
+
+def increment_on_call(filename: str) -> Callable[[Callable, ...], Callable]:
+    def decorator(func: Callable) -> Callable:
+        @wraps(func)
+        def with_increment(*args, **kwargs):
+            increment(filename)
+            return func(*args, **kwargs)
+        return with_increment
+    return decorator

monitoring/docker-compose.yml

@@ -4,10 +4,11 @@ networks:
 
 volumes:
   grafana-storage:
+  py-persistent:
 
 services:
   app_py:
-    image: kolay0ne/app_py:lab8
+    image: kolay0ne/app_py:lab12
     ports:
       - "5000:5000"
     logging:
@@ -17,6 +18,8 @@ services:
       resources: {limits: {memory: 30M}}
     networks:
       - prometheus
+    volumes:
+      - py-persistent:/app/persistent
 
   app_go:
     image: kolay0ne/app_go:lab8