cache: skip non-kickstart treeinfo [RHELDST-24308]

It turns out there is a special case in the current CDN config forcing
a fast 404 response on treeinfo URLs not ending in "/kickstart/treeinfo".
A side-effect of forcing that response is that any requests to cache
flush on such a path will fail, e.g.

    flush /some/kickstart/treeinfo => OK

    flush /some/treeinfo => always fails

As such, we'll need a special case to filter out these paths from any
attempted cache flushes. There is never any need for cache flush if the
response is forced to 404 anyway.

Note this is unlikely to come up in any real publishes of kickstart
repos since those are always using /kickstart in the path.
It came up in the context of migrating some old content to exodus-cdn,
because some files named "treeinfo" exist underneath /origin/files which
will trigger the usual cache flush attempts.

exodus_gw/worker/cache.py

@@ -18,6 +18,18 @@
 LOG = logging.getLogger("exodus-gw")
 
 
+def exclude_path(path: str) -> bool:
+    # Returns True for certain paths which should be excluded from cache flushing.
+    if path.endswith("/treeinfo") and not path.endswith("/kickstart/treeinfo"):
+        # RHELDST-24308: paths matching these conditions get a forced 404 response
+        # without going to the CDN origin. This has the side-effect of breaking
+        # cache flushing for those paths - if we request flush for these paths
+        # we'll get an error.
+        LOG.debug("Skipping %s: treeinfo fast-404 case", path)
+        return True
+    return False
+
+
 class Flusher:
     def __init__(
         self,
@@ -26,7 +38,7 @@ def __init__(
         env: str,
         aliases: list[tuple[str, str]],
     ):
-        self.paths = paths
+        self.paths = [p for p in paths if not exclude_path(p)]
         self.settings = settings
         self.aliases = aliases
 

tests/worker/test_cdn_cache.py

@@ -208,9 +208,12 @@ def test_flush_cdn_cache_typical(
             # - different TTL values for different types of file
             # - leading "/" vs no leading "/" - both should be tolerated
             # - alias resolution
+            # - treeinfo special case
             "/path/one/repodata/repomd.xml",
             "path/two/listing",
             "third/path",
+            "/some/misc/treeinfo",
+            "/some/kickstart/treeinfo",
         ],
         env="cachetest",
         settings=settings,
@@ -242,11 +245,14 @@ def test_flush_cdn_cache_typical(
         # after alias resolution are flushed.
         "S/=/123/4567/10m/cdn1.example.com/path/two-dest/listing cid=///",
         "S/=/123/4567/10m/cdn1.example.com/path/two/listing cid=///",
+        # note only the kickstart treeinfo appears, the other is filtered.
+        "S/=/123/4567/30d/cdn1.example.com/some/kickstart/treeinfo cid=///",
         "S/=/123/4567/30d/cdn1.example.com/third/path cid=///",
         "S/=/123/4567/4h/cdn1.example.com/path/one-dest/repodata/repomd.xml cid=///",
         "S/=/123/4567/4h/cdn1.example.com/path/one/repodata/repomd.xml cid=///",
         "S/=/234/6677/10m/cdn2.example.com/other/path/two-dest/listing x/y/z",
         "S/=/234/6677/10m/cdn2.example.com/other/path/two/listing x/y/z",
+        "S/=/234/6677/30d/cdn2.example.com/other/some/kickstart/treeinfo x/y/z",
         "S/=/234/6677/30d/cdn2.example.com/other/third/path x/y/z",
         "S/=/234/6677/4h/cdn2.example.com/other/path/one-dest/repodata/repomd.xml x/y/z",
         "S/=/234/6677/4h/cdn2.example.com/other/path/one/repodata/repomd.xml x/y/z",
@@ -255,11 +261,13 @@ def test_flush_cdn_cache_typical(
         "https://cdn1.example.com/path/one/repodata/repomd.xml",
         "https://cdn1.example.com/path/two-dest/listing",
         "https://cdn1.example.com/path/two/listing",
+        "https://cdn1.example.com/some/kickstart/treeinfo",
         "https://cdn1.example.com/third/path",
         # Used the CDN URL which had a leading path.
         "https://cdn2.example.com/root/path/one-dest/repodata/repomd.xml",
         "https://cdn2.example.com/root/path/one/repodata/repomd.xml",
         "https://cdn2.example.com/root/path/two-dest/listing",
         "https://cdn2.example.com/root/path/two/listing",
+        "https://cdn2.example.com/root/some/kickstart/treeinfo",
         "https://cdn2.example.com/root/third/path",
     ]