Use redis for saving previous counter values

Author: Anze

Pipfile

@@ -15,6 +15,7 @@ ansicolors = "*"
 easysnmp = {editable = true,git = "http://github.com/grafolean/easysnmp"}
 mathjspy = "*"
 numpy = "*"
+redis = "*"
 
 [requires]
 python_version = "3.6"

Pipfile.lock

@@ -32,3 +32,12 @@ services:
     # on the same host, '127.0.0.1' translates to container, not host - this directive changes network mode
     # so that Docker networking is bypassed.
     network_mode: "host"
+
+  redis:
+    image: redis:5-alpine
+    container_name: grafolean-collector-snmp-redis
+    ports:
+      - "127.0.0.1:6379:6379"
+    # We advise not to use `network_mode: "host"` in production, because it would expose Redis to host network
+    # (even if access is limited to 127.0.0.1).
+    network_mode: "host"

docker-compose.dev.yml

@@ -16,13 +16,16 @@ services:
     environment:
       # Backend url must be set to the address of the Grafolean backend, for example this uses Grafolean hosted service:
       # - BACKEND_URL=https://grafolean.com/api
+      # IMPORTANT: '127.0.0.1' and 'localhost' are _never_ correct addresses for Grafolean backend, because they translate
+      # to container, not host.
       - BACKEND_URL=
       # To use SNMP Collector, a bot with the protocol "snmp" must be added via user interface, then the token needs to be copied here:
       - BOT_TOKEN=
       # Interval between fetching information about jobs:
       - JOBS_REFRESH_INTERVAL=60
+      - REDIS_HOST=redis
     restart: always
-    # Grafolean backend must be accessible on BACKEND_URL *from the point of view of container*. If running
-    # on the same host, '127.0.0.1' translates to container, not host - this directive changes network mode
-    # so that Docker networking is bypassed.
-    network_mode: "host"
+
+  redis:
+    image: redis:5-alpine
+    container_name: grafolean-collector-snmp-redis

docker-compose.yml

@@ -6,6 +6,7 @@
 from pytz import utc
 from colors import color
 import requests
+import redis
 
 from easysnmp import Session, SNMPVariable
 from mathjspy import MathJS
@@ -26,18 +27,19 @@ class NoValueForOid(Exception):
     pass
 
 
-previous_counter_values = {}
+REDIS_HOST = os.environ.get('REDIS_HOST', '127.0.0.1')
+r = redis.Redis(host=REDIS_HOST)
 
 
 def _get_previous_counter_value(counter_ident):
-    prev_value = previous_counter_values.get(counter_ident)
-    if prev_value is None:
+    prev_value = r.hgetall(counter_ident)
+    if not prev_value:  # empty dict
         return None, None
-    return prev_value
+    return int(float(prev_value[b'v'])), float(prev_value[b't'])
 
 
 def _save_current_counter_value(new_value, now, counter_ident):
-    previous_counter_values[counter_ident] = (new_value, now)
+    r.hmset(counter_ident, {b'v': new_value, b't': now})
 
 
 def _convert_counters_to_values(results, now, counter_ident_prefix):