Use custom origins for Cloud CDN when content is hosted on-premises or in another cloud, and you want to deliver the content over Google's high performance, distributed edge caching infrastructure.
The terms "custom origin," "external endpoint," and "internet endpoint" are
often used interchangeably because they have the same meaning.
In CDN, "origin" is the industry-standard term for a backend instance that
serves web content. This document uses the term custom origin.
Supported origins for Cloud CDN
The Cloud CDN (content delivery network) works with HTTP(S) Load Balancing to deliver content to your users. The external HTTP(S) load balancer provides the frontend IP addresses and ports that receive requests. Cloud CDN content can be sourced from various types of backends:
- Instance groups
- Zonal network endpoint groups (NEGs)
- Internet network endpoint groups (NEGs), also known as custom origins. Internet NEGs can be origins hosted within on-premises infrastructure or origins provided by third-party providers (discussed on this page)
- Backend buckets
Hybrid and multi-cloud architectures
As you move your services to Google Cloud, you might need to do so in phases. Sometimes, certain content can't immediately be moved to a cloud environment and might need to stay on-premises. In other cases, the content might be hosted in another cloud. Cloud CDN support for custom origins enables you to use Google's globally distributed edge caching infrastructure for such content.
In the example, images content resides in Google Cloud, while video
resides in a Tokyo data center, which could be on premises or in another cloud.
With custom origins, origins in the Tokyo data center can be
the backend source of the video content with Cloud CDN and
HTTP(S) Load Balancing delivering the content to users.
Using URL maps, this deployment can
direct origin pull requests for video traffic to the custom origin in Tokyo.
This mapping is determined based on request URL: /video.
For images (determined based on request URL: /images), content is sourced
from Google Cloud and is delivered by the Cloud CDN edge
infrastructure.
Cloud CDN and load balancing caveat
Cloud CDN supports fetching content from a single custom origin for a service. It does not provide load balancing among multiple custom origins for a service, nor does it load balance between a custom origin and a Google Cloud backend.
Specifying a custom origin
Similar to configuring Cloud CDN with your endpoints deployed in Google Cloud, you can use the network endpoint groups (NEGs) API to add your server as the custom origin for Cloud CDN.
You need to use an internet NEG to specify the custom origin. An internet NEG has one of the following endpoint types:
| Endpoint address | Type | Definition | When to use |
|---|---|---|---|
| Hostname and an optional port | INTERNET_FQDN_PORT |
A publicly resolvable fully qualified domain name and an optional port,
for example backend.example.com:443 (default ports:
80 for HTTP and 443) |
Use this endpoint when your external origin can be resolved through a fully-qualified domain name with public DNS. |
| IP address and an optional port | INTERNET_IP_PORT |
A publicly accessible IP address and an optional port, for example
8.8.8.8 or 8.8.8.8:443 (default ports:
80 for HTTP and 443) |
Use this endpoint to specify a publicly accessible IP address and a port to connect to. |
The best practice is to create the internet NEG with the INTERNET_FQDN_PORT
endpoint type and an FQDN value as an origin hostname value. This insulates the
Cloud CDN configuration from IP address changes in the origin
infrastructure. Network endpoints that are defined using FQDNs are resolved
through public DNS. Make sure that the configured FQDN is resolvable through
Google Public DNS.
Note that once created, the type cannot be changed between INTERNET_FQDN_PORT and
INTERNET_IP_PORT. You will need to create a new internet NEG and change your
backend service to use the new internet NEG.
When using a custom origin that expects a particular value for the HTTP
request's Host header, you must configure the backend service to set the
Host header to that expected value. If you don't configure a user-defined
request header, a backend service preserves the Host header that the client
used to connect to the Google Cloud external HTTP(S) load balancer. For general
information about user-defined request headers, see Creating user-defined
request headers. For a
specific example, see Configuring a load balancer with a custom
origin.
For Cloud CDN to cache the responses from your origin, your origin must
meet the existing Cloud CDN requirements for
caching, such as setting valid Cache-Control headers in
responses to Cloud CDN and the external HTTP(S) load balancer.
Using custom origins and Google Cloud-based origins
The following figure shows an internet NEG used to deploy a custom origin with HTTP(S) Load Balancing and Cloud CDN.
For more information, see Internet network endpoint groups overview.
What's next
- For instructions showing how to set up a custom origin in an internet NEG, see Setting up an internet NEG.
- For details about what content is cached, see Caching details.
- For resolving issues, see Troubleshooting custom origin and internet NEG issues.