Caching: Optionally configure TTL using environment variable CACHE_TTL

Author: amotl

CHANGES.rst

@@ -7,6 +7,7 @@ in progress
 ===========
 - Explore dashboards: Ignore ``-- Mixed --`` data sources
 - Caching: Increase default cache TTL to five minutes again
+- Caching: Optionally configure TTL using environment variable ``CACHE_TTL``
 
 2023-03-05 0.14.1
 =================

grafana_wtf/commands.py

@@ -105,12 +105,6 @@ def run():
       export GRAFANA_TOKEN=eyJrIjoiWHg...dGJpZCI6MX0=
       grafana-wtf find luftdaten
 
-      # Use infinite cache expiration time, essentially caching forever.
-      grafana-wtf find '#299c46' --cache-ttl=inf
-
-      # Set cache expiration time to zero, essentially disabling the cache.
-      grafana-wtf find geohash --cache-ttl=0
-
       # Search keyword within list of specific dashboards.
       grafana-wtf --select-dashboard=_JJ22OZZk,5iGTqNWZk find grafana-worldmap
 
@@ -139,6 +133,18 @@ def run():
       # Output full history table in Markdown format
       grafana-wtf log --format=tabular:pipe
 
+    Cache control:
+
+      # Use infinite cache expiration time, essentially caching forever.
+      grafana-wtf find '#299c46' --cache-ttl=inf
+
+      # Set cache expiration time to zero, essentially disabling the cache.
+      grafana-wtf find geohash --cache-ttl=0
+
+      # Setting `--cache-ttl` per environment variable `CACHE_TTL` is also possible
+      export CACHE_TTL=infinite
+      grafana-wtf find geohash
+
     """
 
     # Parse command line arguments
@@ -159,11 +165,17 @@ def run():
     grafana_url = options["grafana-url"] or os.getenv("GRAFANA_URL")
     grafana_token = options["grafana-token"] or os.getenv("GRAFANA_TOKEN")
 
+    # Read cache expiration time setting, environment variable takes precedence.
+    if "CACHE_TTL" in os.environ:
+        cache_ttl = os.getenv("CACHE_TTL")
+    else:
+        cache_ttl = options["cache-ttl"]
+
     # Compute cache expiration time.
     try:
-        cache_ttl = int(options["cache-ttl"])
-    except:
-        if not options["cache-ttl"] or "infinite".startswith(options["cache-ttl"].lower()):
+        cache_ttl = int(cache_ttl)
+    except ValueError:
+        if not cache_ttl or "infinite".startswith(cache_ttl.lower()):
             cache_ttl = None
         else:
             raise

grafana_wtf/core.py

@@ -50,9 +50,11 @@ def __init__(self, grafana_url, grafana_token):
 
     def enable_cache(self, expire_after=60, drop_cache=False):
         if expire_after is None:
-            log.info(f"Configure response cache to never expire (infinite caching)")
+            log.info(f"Response cache will never expire (infinite caching)")
+        elif expire_after == 0:
+            log.info(f"Response cache will expire immediately (expire_after=0)")
         else:
-            log.info(f"Configure response cache to expire after {expire_after} seconds")
+            log.info(f"Response cache will expire after {expire_after} seconds")
         requests_cache.install_cache(expire_after=expire_after, use_cache_dir=True)
         cache_database_file = requests_cache.get_cache().db_path
         log.info(f"Response cache database location is {cache_database_file}")

tests/conftest.py

@@ -22,7 +22,7 @@
 
 # Make sure development or production settings don't leak into the test suite.
 def clean_environment():
-    for envvar in ["GRAFANA_URL", "GRAFANA_TOKEN"]:
+    for envvar in ["GRAFANA_URL", "GRAFANA_TOKEN", "CACHE_TTL"]:
         try:
             del os.environ[envvar]
         except KeyError: