Enable caching of blobs in V2 registry protocol, to avoid DB connections after the cache has been loaded

This should help for bursty pull traffic, as it will avoid DB connections on a huge % of requests

endpoints/v2/blob.py

@@ -7,9 +7,10 @@ from flask import url_for, request, redirect, Response, abort as flask_abort
 import bitmath
 import resumablehashlib
 
-from app import storage, app, get_app_url, metric_queue
+from app import storage, app, get_app_url, metric_queue, model_cache
 from auth.registry_jwt_auth import process_registry_jwt_auth
 from data import database
+from data.cache import cache_key
 from digest import digest_tools
 from endpoints.decorators import anon_protect, parse_repository_name
 from endpoints.v2 import v2_bp, require_repo_read, require_repo_write, get_input_stream
@@ -33,6 +34,18 @@ class _InvalidRangeHeader(Exception):
   pass
 
 
+def _get_repository_blob(namespace_name, repo_name, digest):
+  """ Returns the blob with the given digest under the repository with the given
+      name. If one does not exist (or it is still uploading), returns None.
+      Automatically handles caching.
+  """
+  def load_blob():
+    return model.get_blob_by_digest(namespace_name, repo_name, digest)
+
+  blob_cache_key = cache_key.for_repository_blob(namespace_name, repo_name, digest)
+  return  model_cache.retrieve(blob_cache_key, load_blob)
+
+
 @v2_bp.route(BLOB_DIGEST_ROUTE, methods=['HEAD'])
 @parse_repository_name()
 @process_registry_jwt_auth(scopes=['pull'])
@@ -41,7 +54,7 @@ class _InvalidRangeHeader(Exception):
 @cache_control(max_age=31436000)
 def check_blob_exists(namespace_name, repo_name, digest):
   # Find the blob.
-  blob = model.get_blob_by_digest(namespace_name, repo_name, digest)
+  blob = _get_repository_blob(namespace_name, repo_name, digest)
   if blob is None:
     raise BlobUnknown()
 
@@ -49,7 +62,8 @@ def check_blob_exists(namespace_name, repo_name, digest):
   headers = {
     'Docker-Content-Digest': digest,
     'Content-Length': blob.size,
-    'Content-Type': BLOB_CONTENT_TYPE,}
+    'Content-Type': BLOB_CONTENT_TYPE,
+  }
 
   # If our storage supports range requests, let the client know.
   if storage.get_supports_resumable_downloads(blob.locations):
@@ -67,7 +81,7 @@ def check_blob_exists(namespace_name, repo_name, digest):
 @cache_control(max_age=31536000)
 def download_blob(namespace_name, repo_name, digest):
   # Find the blob.
-  blob = model.get_blob_by_digest(namespace_name, repo_name, digest)
+  blob = _get_repository_blob(namespace_name, repo_name, digest)
   if blob is None:
     raise BlobUnknown()