Optimizing cache performance and managing content delivery involves configuring Cloud CDN to serve content efficiently from external origins and third-party object storage. The goal is to maximize cache hit ratios, control content freshness, and ensure secure, low-latency delivery while meeting specific workload requirements.
Cache modes determine how Cloud CDN respects or overrides origin cache directives for content served from external backends, including internet network endpoint groups (NEGs) and third-party storage. The three primary modes are USE_ORIGIN_HEADERS, CACHE_ALL_STATIC, and FORCE_CACHE_ALL. Choose USE_ORIGIN_HEADERS when you want the origin's HTTP Cache-Control headers to dictate caching behavior fully. Choose CACHE_ALL_STATIC to cache all static content automatically, even if the origin sends no cache headers, which is useful for simple object storage. Choose FORCE_CACHE_ALL to cache all responses, including dynamic content, overriding any origin Cache-Control headers that might prevent caching; use this mode cautiously, as it can lead to serving stale dynamic data.
A cache key is the unique identifier Cloud CDN uses to store and retrieve a cached object. By default, the full request URL, including host, path, and all query parameters, forms the key. For external origins, you can create custom cache keys to optimize caching. For example, you can configure the key to exclude the host field if multiple domains serve identical content, consolidating cache entries. You can also exclude specific query strings used for tracking that do not affect content, or include only versioning parameters. This reduces unnecessary cache sharding and improves the cache hit ratio by ensuring that requests for the same logical resource map to the same cache entry.
Time-to-live (TTL) settings control how long content remains in the cache before it is considered stale. You can configure default TTLs and override them based on response codes for external backends. Negative caching allows you to cache error responses (like HTTP 404 or 5xx) for a specified duration. This shields your origin from repeated requests for missing or failing resources, reducing load and improving client response times. For example, you can set a short TTL for 404 errors to allow for quick recovery if a resource becomes available, while setting a longer TTL for 5xx errors during an origin outage.
To optimize cache performance, you must monitor Cloud CDN operations using Cloud Logging and Cloud Monitoring. Enable logging for all CDN-enabled backends to capture detailed request data. Key log fields include cacheId (identifying the cache location), cacheStatus (showing hit, miss, or revalidated states), and cacheKeyFingerprint. You can filter logs to analyze cache hit ratios and identify patterns leading to misses. Use the Cloud CDN custom monitoring dashboard to visualize metrics like cache fill latency, egress, and error rates. Reviewing these insights helps you tune cache policies, TTLs, and invalidation strategies.
Cache invalidation forcibly removes content from Cloud CDN edge caches before its TTL expires. Use invalidation sparinglyâonly for legal takedowns or critical incorrect uploadsâas it is rate-limited and eventually consistent. For routine updates, prefer content versioning techniques: change the filename (file_v2.css), path (/v2/file.css), or use a cache-key-included query parameter. This creates a new cache entry, allowing old versions to expire naturally. When updating existing files on an origin, make updates atomicallyâupload to a temporary name and rename after completionâto prevent clients from caching partially written files during the upload process.
Integrating third-party object storage as a CDN origin involves configuring Cloud CDN to fetch content from external HTTP-based origins such as AWS S3 or Azure Blob Storage, rather than from Google Cloud native storage. Cloud CDN supports external backends through internet network endpoint groups (NEGs), which allow the load balancer to route requests to origins hosted outside of Google Cloud, whether in other cloud providers or on-premises data centers. This capability enables organizations to leverage existing storage infrastructure while benefiting from Google's global edge-caching network. When a cache miss occurs, Cloud CDN forwards the request to the configured external origin, caches the response, and serves subsequent requests from the nearest edge location.
Cloud CDN can use external backends as origins through internet NEGs, which define the IP addresses or hostnames of third-party object storage endpoints. The external backend must be publicly accessible via HTTPS, as Cloud CDN communicates with origins over HTTP/HTTPS protocols. When configuring an internet NEG, you specify the fully qualified domain name of the third-party storage service, such as s3.amazonaws.com for AWS S3 or blob.core.windows.net for Azure Blob Storage. The origin configuration also includes settings for connection timeouts, read timeouts, and response timeouts that control how long Cloud CDN waits for the origin to respond. Internet NEGs support both HTTP and HTTP/2 protocols, but Cloud CDN does not automatically fall back to HTTP/1.1 unless explicitly configured.
Cloud CDN uses the complete request URL as the default cache key, which means that query strings, host headers, and protocol all influence what content is served from cache. For third-party object storage origins, you can customize cache keys to include or exclude specific components based on your content versioning strategy. If your storage solution uses query string parameters for versioning (such as file.css?v=2), you must configure Cloud CDN to include those parameters in the cache key, otherwise different versions may be served incorrectly. Alternatively, you can implement versioning through file naming conventions (such as file_v2.css) or path modifications (such as /v2/file.css), which naturally create separate cache entries without requiring query string configuration. The cache key configuration directly impacts cache hit ratios and origin request frequency.
When serving web content through Cloud CDN that will be accessed by browsers on different domains, you must configure CORS headers on the third-party origin to allow cross-origin requests. The origin server must include appropriate Access-Control-Allow-Origin headers in its responses, and may also need to specify Access-Control-Allow-Methods, Access-Control-Allow-Headers, and Access-Control-Max-Age for preflight request handling. Cloud CDN passes through these headers from the origin to clients, so the CORS policy is determined by the third-party storage configuration rather than by Cloud CDN itself. For AWS S3, this involves setting CORS configuration on the S3 bucket; for Azure Blob Storage, you configure CORS rules in the storage account settings. Improper CORS configuration results in browsers blocking content loaded from Cloud CDN.
Securing access between Cloud CDN and third-party object storage requires configuring appropriate authentication mechanisms on the origin side. For AWS S3, this typically involves using AWS Signature Version 4 to authenticate requests, where Cloud CDN presents signed requests that include authentication headers computed using AWS access keys. Azure Blob Storage supports shared access signatures (SAS) or account keys for authentication. The origin authentication ensures that only valid Cloud CDN requests can fetch content, preventing direct access to the third-party storage if desired. Additionally, you can implement defense-in-depth by using private buckets with origin authentication, which blocks any requests that bypass Cloud CDN. Cloud CDN logs can be used to monitor origin access patterns and detect any unauthorized access attempts.
An internet Network Endpoint Group (NEG) architecture allows Google Cloud services to route traffic to external HTTP(S) endpoints and third-party storage systems outside Google Cloud. This architecture connects an external Application Load Balancer and Cloud CDN to external backends using dedicated backend services. By coupling these components, organizations can deliver globally cached content while enforcing central routing and security rules.
An external Application Load Balancer serves as the public entry point for incoming client traffic directed toward external endpoints. The load balancer relies on a frontend configurationâconsisting of a global external IP address, forwarding rules, and a target HTTP(S) proxyâthat passes requests to a URL map. The URL map evaluates the hostname and path of each incoming request to route traffic to the appropriate backend service.
A backend service defines how the load balancer communicates with and distributes traffic across its attached backend endpoints. Each backend service connects to backends such as NEGs and manages operational settings, including balancing modes, capacity targets, and protocol options like HTTP, HTTPS, or HTTP/2. Health checks can be associated with backend services to continuously probe endpoints, ensuring that traffic is directed only to healthy targets while automatically removing unhealthy endpoints from the active pool.
Google Cloud Armor provides Layer 7 filtering and threat mitigation for backend services that have Cloud CDN enabled. Deploying Cloud Armor alongside Cloud CDN protects origin servers from web application attacks and helps mitigate OWASP Top 10 security risks. Access controls and filtering rules are enforced using two distinct policy types:
When an organization attaches both edge and backend policies to the same backend service, traffic flows through edge filtering first. Cache misses that satisfy the edge security rules then pass to the backend security policy for origin evaluation. This two-tier model prevents unauthorized requests from consuming origin capacity while ensuring cached assets are screened before delivery.
A URL map directs client traffic to distinct backend services based on host rules and path matchers. This routing structure allows a single load balancer frontend to distribute traffic across different backend services, such as separating product pages from dynamic API endpoints. Organizations can also use cross-project service referencing to link a centralized frontend and URL map in one project to backend services located in other service projects within the same organization.
To maintain user state, a backend service can enforce session affinity, which maps requests from a specific client to the same backend target as long as that endpoint remains healthy and under capacity. Session affinity can break if the backend pool changes, such as when endpoints fail health checks or when administrators add or remove endpoints from the backend group. Load balancing algorithms evaluate traffic distribution across healthy endpoints to ensure reliable failover whenever an individual target becomes unreachable.
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StudyCertsUSE_ORIGIN_HEADERS (respects origin headers), CACHE_ALL_STATIC (caches all static content automatically), and FORCE_CACHE_ALL (caches everything including dynamic content).Edge security policies filter traffic at the network edge before content is served from the Cloud CDN cache, while backend security policies apply filtering only to dynamic requests and cache misses that pass through to the origin. When both are attached, edge filtering runs first, and cache misses that pass the edge rules then go through backend evaluation before reaching the origin.
You must configure Cloud CDN to include the query string parameters in the cache key. By default, the full URL including query strings forms the cache key, but if you have customized your cache key to exclude query strings, you need to explicitly include the versioning parameters (like ?v=2) in the cache key configuration so that different versions create separate cache entries.
Cloud CDN uses AWS Signature Version 4 to authenticate requests to AWS S3. This involves computing authentication headers using AWS access keys that you configure, allowing Cloud CDN to present signed requests that S3 accepts as valid.
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