Mapping resource

Get traffic from the edge

The core Emissary resource used to manage cluster ingress is the Mapping resource.

A Mapping resource routes a URL path (or prefix) to a service (either a Kubernetes service or other web service).

Examples

This Mapping would route requests to https://<hostname>/webapp/ to the webapp-svc Service.

---
apiVersion: getambassador.io/v2
kind:  Mapping
metadata:
  name:  webapp-mapping
spec:
  prefix: /webapp/
  service: webapp-svc

Here’s another example using a web service that maps requests to /httpbin/ to http://httpbin.org:

---
apiVersion: getambassador.io/v2
kind:  Mapping
metadata:
  name:  httpbin-mapping
spec:
  prefix: /httpbin/
  service: http://httpbin.org

Applying a Mapping resource

A Mapping resource can be managed using the same workflow as any other Kubernetes resources (like a Service or Deployment). For example, if the above Mapping is saved into a file called httpbin-mapping.yaml, the following command will apply the configuration directly to Emissary:

kubectl apply -f httpbin-mapping.yaml

For production use, best practice is to store the file in a version control system and apply the changes with a continuous deployment pipeline. The Ambassador Operating Model provides more detail.

Resources

To Emissary, a resource is a group of one or more URLs that all share a common prefix in the URL path. For example, these URLs all share the /resource1/ path prefix, so /resource1/ can be considered a single resource:

• https://ambassador.example.com/resource1/foo
• https://ambassador.example.com/resource1/bar
• https://ambassador.example.com/resource1/baz/zing

On the other hand, these URLs share only the prefix / – you could tell Emissary to treat them as a single resource, but it’s probably not terribly useful.

• https://ambassador.example.com/resource1/foo
• https://ambassador.example.com/resource2/bar
• https://ambassador.example.com/resource3/baz/zing

Note that the length of the prefix doesn’t matter; a prefix like /v1/this/is/my/very/long/resource/name/ is valid.

Also note that Emissary does not actually require the prefix to start and end with / – however, in practice, it’s a good idea. Specifying a prefix of /man would match all of the following, which probably is not what was intended:

• https://ambassador.example.com/man/foo
• https://ambassador.example.com/mankind
• https://ambassador.example.com/man-it-is/really-hot-today

Services

Emissary routes traffic to a service. A service is defined as [scheme://]service[.namespace][:port]. Everything except for the service is optional.

• scheme can be either http or https; if not present, the default is http.
• service is the name of a service (typically the service name in Kubernetes or Consul); it is not allowed to contain the . character.
• namespace is the namespace in which the service is running. Starting with Emissary 1.0.0, if not supplied, it defaults to the namespace in which the Mapping resource is defined. The default behavior can be configured using the Module resource. When using a Consul resolver, namespace is not allowed.
• port is the port to which a request should be sent. If not specified, it defaults to 80 when the scheme is http or 443 when the scheme is https. Note that the resolver may return a port in which case the port setting is ignored.

While using service.namespace.svc.cluster.local may work for Kubernetes resolvers, the preferred syntax is service.namespace.

Extending Mappings

Mapping resources support a rich set of annotations to customize the specific routing behavior. Here’s an example service for implementing the CQRS pattern (using HTTP):

---
apiVersion: getambassador.io/v2
kind:  Mapping
metadata:
  name:  cqrs-get
spec:
  prefix: /cqrs/
  method: GET
  service: getcqrs
---
apiVersion: getambassador.io/v2
kind:  Mapping
metadata:
  name:  cqrs-put
spec:
  prefix: /cqrs/
  method: PUT
  service: putcqrs

Best Practices

Emissary’s configuration is assembled from multiple YAML blocks which are managed by independent application teams. This implies that certain best practices should be followed.

Emissary’s configuration should be under version control.

While you can always read back the Emissary’s configuration from Kubernetes or its diagnostic service, the Emissary will not do versioning for you.

Emissary tries to not start with a broken configuration, but it’s not perfect.

Gross errors will result in the Emissary refusing to start, in which case kubectl logs will be helpful. However, it’s always possible to map a resource to the wrong service, or use the wrong rewrite rules. Emissary can’t detect that on its own, although its diagnostic service can help you figure it out.

Be careful of mapping collisions.

If two different developers try to map /myservice/ to something, this can lead to unexpected behavior. Emissary’s canary deployment logic means that it’s more likely that traffic will be split between them than that it will throw an error – again, the diagnostic service can help you here.

Unless specified, mapping attributes cannot be applied to any other resource type.

What’s next?

There are many options for advanced mapping configurations, with features like automatic retries, timeouts, rate limiting, redirects, and more.