Service Extensions enables Application Load Balancers to send callouts to backend services to inject custom processing in the processing path. Traffic extensions run last in the request processing path and first in the response processing path to modify headers and payloads without impacting the choice of the backend service. This page describes how to configure traffic extensions.
For an overview about Application Load Balancer extensions, see Cloud Load Balancing extensions overview.
Introduction
A traffic extension for an Application Load Balancer points to the following resources:
- A forwarding rule to attach to
- A callout backend service whose backends run the
ext_proc
gRPC API
A traffic extension groups related extension services into one or more chains. Each extension chain selects the traffic to act on by using Common Expression Language (CEL) match conditions. The load balancer evaluates a request against each chain's match condition in a sequential manner. When a request matches the conditions defined by a chain, all extensions in the chain act on the request. Only one chain matches a given request.
For information about the limits related to extensions, see the Quotas and limits page.
The extension references the load balancer forwarding rule to attach to. After you configure the resource, the load balancer starts sending matching requests to extension services.
Before you begin
Create the required resources as described in Configure a callout backend service.
Configure a traffic extension
The following example helps you configure a traffic extension to call when the
host matches example.com
. The traffic extension server in the callout-vm
adds a response header, hello: service-extensions
, to matching requests.
Check if there's a match for
example.com
in the URL map.Establish an SSH connection to the client VM.
Console
- In the Google Cloud console, go to the VM instances page.
- In the list of virtual machine instances, click SSH in the row of the instance that you want to connect to.
gcloud
Use the
gcloud compute ssh
command.gcloud compute ssh CLIENT_VM \ --zone=ZONE
Replace the following:
CLIENT_VM
: the name of the client VMZONE
: the zone of the VM
Run the following
curl
command against the forwarding rule in the client VM:curl -D - -H "host: example.com" FORWARDING_RULE_IP
Replace FORWARDING_RULE_IP with the IP address of the forwarding rule. To find the IP address, use the
gcloud compute forwarding-rules describe
command.The output is similar to the following:
HTTP/1.1 200 OK ... content-length: 46 content-type: text/html via: 1.1 google Page served from: l7-ilb-backend-example-1c7t
Close the SSH connection.
Configure the traffic extension.
Console
In the Google Cloud console, go to the Service Extensions page.
Click Create extension.
A wizard opens to guide you through some initial steps.
For the product, select Load Balancing. Then, click Continue.
A list of Application Load Balancers that support extensions appears.
Select a load balancer type. For regional load balancers, also specify the region. Click Continue.
For the service extension type, select Traffic extensions, click Continue, and then click Done.
The Create service extension form opens. Notice that the preceding selections, which appear at the top of the page, are not editable.
In the Basics section, do the following:
Specify a unique name for the service extension.
The name must start with a lowercase letter followed by up to 62 lowercase letters, numbers, or hyphens and must not end with a hyphen.
Optional: Enter a brief description about the extension by using up to 1,024 characters.
Optional: In the Labels section, click Add label. Then, in the row that appears, do the following:
- For Key, enter a key name.
- For Value, enter a value for the key.
To add more key-value pairs, with the maximum limit being 64, click Add label.
For more information about labels, see Create and update labels for projects.
For Forwarding rules, select one or more forwarding rules to associate with the extension.
Forwarding rules that are already associated with another extension cannot be selected and appear unavailable.
For Extension chains, add one or more extension chains to execute for a matching request.
To add an extension chain, click Add an extension chain, do the following, and then click Done:
For Extension chain name, specify a unique name.
The name must conform with RFC-1034, use only lowercase letters, numbers, and hyphens, and have a maximum length of 63 characters. Additionally, the first character must be a letter and the last character must be a letter or a number.
To match requests for which the extension chain is executed, for Match condition, specify a Common Expression Language (CEL) expression.
For more information, click Get syntax help or see CEL matcher language reference.
Add one or more extensions to execute for a matching request.
For each extension, under Extensions, do the following, and then click Done:
For Extension name, specify a unique name.
The name must conform with RFC-1034, use only lower-case letters, numbers, and hyphens, and have a maximum length of 63 characters. Additionally, the first character must be a letter and the last character must be a letter or a number.
For Authority, enter the
authority
header from the gRPC request sent from Envoy to the extension service.For Backend service, select a backend service created by following the instructions in Configure a callout backend service.
For Timeout, specify a value between 10 and 1000 milliseconds after which a message on the stream times out.
For Events, select one or more HTTP event types that call the extension.
For Forward headers, click Add header, and then add HTTP headers to forward to the extension (from the client or the backend). If a header is not specified, all headers are sent.
For Fail open, select Enabled. If the call to the extension fails or times out, request or response processing continues without error. Any subsequent extensions in the extension chain are also run.
By default, the Fail open field is not selected. In this case, if response headers have not been delivered to the downstream client, a generic
500
status code is returned to the client. If response headers have been delivered, the HTTP stream to the downstream client is reset.
Click Create extension.
gcloud
Define the extension in a YAML file and associate it with the forwarding rule. Use the sample values provided.
cat >traffic.yaml <<EOF name: traffic-ext forwardingRules: - https://www.googleapis.com/compute/v1/projects/PROJECT_ID/regions/us-west1/forwardingRules/l7-ilb-forwarding-rule loadBalancingScheme: INTERNAL_MANAGED metadata: {"fr": "{forwarding_rule_id}", "key2": {"key3":"value"}} extensionChains: - name: "chain1" matchCondition: celExpression: 'request.host == "example.com"' extensions: - name: 'ext11' authority: ext11.com service: https://www.googleapis.com/compute/v1/projects/PROJECT_ID/regions/us-west1/backendServices/l7-ilb-callout-service failOpen: false timeout: 0.1s supportedEvents: - RESPONSE_HEADERS EOF
Replace
PROJECT_ID
with the project ID.The
metadata
field in the extension configuration lets you pass any JSON objects from the load balancer to the extension server. The metadata is sent in aProcessingRequest
message and encoded by using aprotobuf.Struct
type. Any text within the JSON object that matches the specified forwarding rule ID is replaced with the fully qualified resource URL of the forwarding rule associated with the client request.Import the traffic extension. Use the
gcloud service-extensions lb-traffic-extensions import
command with the following sample values.gcloud service-extensions lb-traffic-extensions import traffic-ext \ --source=traffic.yaml \ --location=us-west1
Verify that the traffic extension works as expected. Establish an SSH connection to the VM client and use the same
curl
command:curl -D - -H "host: example.com" FORWARDING_RULE_IP
The output includes the
hello: service-extensions
response header.HTTP/1.1 200 OK ... content-length: 46 content-type: text/ hello: service-extensions via: 1.1 google Page served from: l7-ilb-backend-example-1c7t
To validate that the extension targets only
example.com
traffic, repeat thecurl
command without thehost
header.curl -D - FORWARDING_RULE_IP
The output is similar to the following:
HTTP/1.1 200 OK ... content-length: 46 content-type: text/html via: 1.1 google Page served from: l7-ilb-backend-example-1c7t
Limitations for traffic extensions
Cross-project referencing between extensions and the forwarding rule is not supported.
What's next
- View Python and Go samples of
ext-proc
servers in the Service Extensions GitHub repository. - Configure route extensions
- Manage extensions