External HTTP(S) Load Balancing supports advanced traffic management functionality that enables you to use the following features:
- Traffic steering. Intelligently route traffic based on HTTP(S) parameters:
- Traffic actions. Perform request-based actions:
- Traffic policies. Fine-tune load balancing behavior:
You configure these features using the load balancer's URL map. For background information, see the following topics:
Traffic management components
At a high level, external HTTP(S) load balancers provide traffic management by using global URL maps.
The load balancer provides the following mutually exclusive primary actions:
- Route requests to a backend service
- Perform a redirect
When you set up a load balancer, you can configure a URL rewrite action before the load balanacer sends requests to the backend service or backend bucket.
Rewrites or redirects can be applied at three levels in the URL map:
- At the
pathRulewhere the action takes effect when a path is matched
- At the
pathMatcherwhere the action takes effect when no paths are matched for this
- At the
urlMapwhere the action takes effect when none of the hosts specified in any of the host rules are matched
routeRules in a
pathMatcher is an alternative to using
routeRules cannot both appear in the same
pathRules, where order doesn't matter,
routeRules are examined in
routeRule can test the URL path, HTTP headers, and URL query
Use case examples
Traffic management addresses many use cases. This section provides a few high-level examples.
URL rewrites allow you to present external users with URLs that are different from the URLs that your services use.
A URL rewrite separates a URL from a resource. You can translate from human-friendly URLs, which are easier for users to remember and use, transforming them into search-engine friendly URLs, which are easier for search engines to find, or into internal implementation-specific URLs.
The HTTP(S) Load Balancing URL rewrite feature:
- Reads the incoming URL in the request.
- Replaces the host, the path, or both the host and the path, transforming the URL before directing traffic to the backend service or backend bucket.
In the following diagram:
- A user in Japan sends a request for the URL
- When the request reaches the external HTTP(S) load balancer, the load balancer uses
information in the URL map to rewrite the URL to
- (Optional) In this example, the URL map sends the request to an external backend.
For a configuration example, see Rewrites.
With URL redirects, you can redirect client requests from one URL to another URL.
This includes the capability to:
- Redirect all HTTP requests to HTTPS requests.
- Redirect to a different URL formed by modifying the host, path, or both the host and path portion of the URL, and either stripping out or retaining any query parameters.
- Choose which redirect response codes to issue.
Use URL redirects to:
- Provide URL shortening. Client-facing URLs can be made substantially shorter. This service issues a redirect to the web page with the long URL.
- Prevent broken links when web pages are moved or become outdated.
- Allow multiple domain names belonging to the same owner to refer to a single web site.
- Avoid the toil and inefficiencies of configuring workarounds at the backend server to support the necessary redirect.
- Reduce latency. Redirects created at the edge can result in lower latency compared to redirects created at the backend endpoints.
HTTP-to-HTTPS redirects further specifically help you to:
- Meet compliance requirements (such as HIPAA) for encrypted traffic.
- Redirect requests using HTTPS instead of rejecting requests sent with the HTTP protocol.
- Improves the security profile of your application by redirecting the traffic at the layer-7 load balancer itself, as opposed to implementing the redirect at the backend server.
In the following diagram:
- A user in Japan sends a
- Based on the redirect defined in the URL map, the load balancer sends back
HTTP/1.1 302 Found Location: https://example.com/img1redirect, redirecting the HTTP request to an HTTPS request.
- The user's browser sends a
For a configuration example, see Redirects.
Supported response codes
The supported redirect response codes are listed in the table.
|PERMANENT_REDIRECT||308||In this case, the request method is retained.|
|TEMPORARY_REDIRECT||307||In this case, the request method is retained.|
Header-based and parameter-based routing
Header-based and parameter-based routing allow a load balancer to make routing decisions that are based on HTTP headers and URL query parameters.
With this feature, you can simplify your cloud architecture, without deploying additional tiers of proxies (NGINX, for example) to do routing.
You can use the external HTTP(S) load balancer to do the following:
- A/B testing
- Assigning customers to different sets of services running on backends
- Delivering different pages and experiences based on different categories of devices from which the requests originate
pathMatcher is selected based on the host string, the
pathMatcher select a URL path. For more information, see the URL maps
Example: Configuring A/B testing with query parameter-based routing
The following example shows how to do A/B testing by matching on the query string to specify the experiment and input.
Suppose that you want to make sure that requests are handled as follows:
- All requests with the query parameter value
Ago to the backend service called
- All requests with the query parameter value
Bgo to the backend service called
These requirements are summarized in the following table.
To configure this in your global URL map, you can create the following settings.
For a configuration example, see Header-based and parameter-based routing.
Routing requests to backends
In HTTP(S) Load Balancing, the backend for your traffic is determined by using a two-phased approach:
The load balancer selects a backend service with backends. The backends can be the following:
- Compute Engine virtual machine (VM) instances in an unmanaged instance group
- Compute Engine VMs in a managed instance group (MIG)
- Containers by means of a Google Kubernetes Engine (GKE) node in a zonal network endpoint group (NEG)
- External backends outside of Google Cloud in an internet NEG
- Cloud Storage in backend buckets
- App Engine, Cloud Functions, or Cloud Run services in a serverless NEG
The load balancer chooses a backend service based on rules defined in a global URL map.
The backend service selects a backend instance based on policies defined in a global backend service.
When you configure routing, you can choose between the following modes:
- Simple host and path testing, by using
- Advanced request testing, by using
For each URL map, you can choose to use simple host and path rules or advanced host, path, and route rules. The two modes are mutually exclusively. Each URL map can contain only one mode or the other mode.
Simple host and path rule
In a simple host and path rule, URL maps work as described in the URL map overview.
The following diagram shows the logical flow of a simple host and path rule.
A request is initially evaluated by using host rules. A host is the domain
specified by the request. If the request
host matches one of the entries in
hosts field, the associated path matcher is used.
Next, the path matcher is evaluated. Path rules are evaluated on the longest-path-matches-first basis, and you can specify path rules in any order. After the most specific match is found, the request is routed to the corresponding backend service. If the request does not match, the default backend service is used.
A typical simple host and path rule might look something like the following,
where video traffic goes to
video-backend-service, and all other traffic goes
$ gcloud compute url-maps describe ext-https-map
defaultService: global/backendServices/web-backend-service hostRules: - hosts: - '*' pathMatcher: pathmap name: ext-https-map pathMatchers: - defaultService: global/backendServices/web-backend-service name: pathmap pathRules: - paths: - /video - /video/* service: global/backendServices/video-backend-service
For a configuration example, see Host and path.
Advanced host, path, and route rule
Advanced host, path, and route rules provide additional configuration options compared to simple host and path rules. These options enable more advanced traffic management patterns and also modify some of the semantics. For example, route rules are executed in order (rather than by using longest-path-matches-first semantics).
As in the earlier simple host and path rule example, you can configure
advanced traffic management by using a global URL map, but instead of using
pathMatchers.pathRules, you use
The following sections explain the advanced host, path, and route rule components.
When a request reaches your load balancer, the request's
host field is
evaluated against the
hostRules defined in the URL map. Each host rule
consists of a list of one or more hosts and a single path matcher
pathMatcher). If no
hostRules are defined, the request is routed to the
For more information, see
defaultService in the
global URL map API documentation.
After a request matches a host rule, the load balancer evaluates the path matcher corresponding to the host.
A path matcher is made up of the following:
- One or more path rules (
pathRules) or route rules (
A default rule that executes when no other backend services match. The rule has the following mutually exclusive options:
- A default service specifies the default backend service to route to when no other backend services match.
- A default redirect specifies the URL to redirect to when no other backend services match.
When the load balancer is configured for a default service, it can additionally be configured to rewrite the URL before sending the request to the default service.
For more information, see
pathMatchers.routeRules in the global URL map API
Path rules (
pathRules) specify one or more URL paths, such as
Path rules are generally intended for the type of simple host and path-based
routing described previously.
For more information, see
pathRules in the global URL map API
A route rule (
routeRules) matches information in an incoming request and makes
a routing decision based on the match.
Route rules can contain a variety of different match rules (
matchRules) and a
variety of different route actions (
A match rule evaluates the incoming request based on the HTTP(S) request's path, headers, and query parameters. Match rules support various types of matches (for example, prefix match) as well as modifiers (for example, case insensitivity). This enables you to, for example, send HTTP(S) requests to a set of backends based on the presence of a custom-defined HTTP header.
For a detailed list of options supported by
matchRules in the global URL map API
If you have multiple route rules, the load balancer executes them in order, which allows you to specify custom logic for matching, routing, and other actions.
Within a given route rule, when the first match is made, the load balancer stops evaluating the match rules, and any remaining match rules are ignored.
Google Cloud performs the following actions:
- Looks for the first match rule that matches the request.
- Stops looking at any other match rules.
- Applies the actions in the corresponding route actions.
Route rules have several components, as described in the following table.
|Route rule component (
||A number from 0 through 2,147,483,647 (that is, (2^31)-1) assigned to a
route rule within a given path matcher to determine the order of route
The highest priority is
Priority numbers can have gaps; they don't need to be contiguous. You cannot create multiple rules with the same priority.
||An optional description of up to 1,024 characters.|
||The full or partial URL of the backend service resource to which traffic is directed if this rule is matched.|
|Match rules (
||One or more rules that are evaluated against the request. These
|Route action (
||Allows you to specify a URL rewrite action to take when the match rule criteria are met.|
|Redirect action (
||You can configure an action to respond with an HTTP redirect when the match rule criteria are met. This field cannot be used in conjunction with a route action.|
For more information, see the following fields in the global URL map API documentation:
Match rules (
matchRules) match one or more attributes of a request and take
actions specified in the route rule. The following list provides some examples
of request attributes that can be matched by using match rules:
Host: A host name is the domain name portion of a URL; for example, the host name portion of the URL
example.net. In the request, the host name comes from the
Hostheader, as shown in this example curl command, where
10.1.2.9is the load-balanced IP address:
curl -v http://10.1.2.9/video/hd --header 'Host: example.com'
Paths follow the host name; for example
/images. The rule can specify whether the entire path or only the leading portion of the path needs to match.
Other HTTP request parameters, such as HTTP headers, which allow cookie matching, as well as matching based on query parameters (GET variables). Note that regular expression matching for header values isn't supported.
For a complete list of supported match rules, see
pathMatchers.routeRules.matchRules in the global URL map API
Configuring traffic management
You can use the Cloud Console,
gcloud, or the Cloud Load Balancing API to
configure traffic management. Within your chosen configuration environment, you
set up traffic management by using YAML configurations.
For help writing these YAML files, you can use the following resources:
Provides a full list of fields, including semantics regarding relationships, restrictions, and cardinality.
Examples on the traffic management set up page: