Ambassador Concepts

At the heart of Ambassador are the ideas of mappings, modules, and consumers:

  • Mappings associate REST resources with Kubernetes services. Ambassador must have one or more mappings defined to provide access to any services at all.

  • Modules let you enable and configure special behaviors for Ambassador, in ways which may apply to Ambassador as a whole or which may apply only to some mappings. For example, the authentication module allows Ambassador to require authentication per mapping.

  • Consumers represent human end users of Ambassador, and may be required for some modules to function. For example, the authentication module may require defining consumers to let Ambassador know who's allowed to authenticate.

Mappings

Mappings associate REST resources with Kubernetes services. A resource, here, is a group of things defined by a URL profix; a service is exactly the same as in Kubernetes. Ambassador must have one or more mappings defined to provide access to any services at all.

Each mapping can also specify a rewrite rule which modifies the URL as it's handed to the Kubernetes service, and a set of module configuration specific to that mapping

Defining Mappings

You use PUT requests to the admin interface to map a resource to a service:

curl -XPUT -H "Content-Type: application/json" \
      -d <mapping-dict> \
      http://localhost:8888/ambassador/mapping/<mapping-name>

where <mapping-name> is a unique name that identifies this mapping, and <mapping-dict> is a dictionary that defines the mapping:

{
    "prefix": <url-prefix>,
    "service": <service-name>,
    "rewrite": <rewrite-as>,
    "modules": <module-dict>
}
  • <url-prefix> is the URL prefix identifying your resource
  • <service-name> is the name of the service handling the resource
  • <rewrite-as> (optional) is what to replace the URL prefix with when talking to the service
  • <module-dict> (optional) defines any relevant module configuration for this mapping.

You can get a list of all the mappings that Ambassador knows about with

curl http://localhost:8888/ambassador/mapping

and you can delete a specific mapping with

curl -XDELETE http://localhost:8888/ambassador/mapping/<mapping-name>

You can manipulate specific bits of module information for this mapping, as well (the modules section has more on this):

curl http://localhost:8888/ambassador/mapping/<mapping-name>/module/<module-name>

to read a single module's config;

curl -XPUT -H "Content-Type: application/json" \
     -d <module-dict> \
     http://localhost:8888/ambassador/mapping/<mapping-name>/module/<module-name>

to alter a single module's config (<module-dict> is the dictionary of new configuration information for the given mapping and module); and

curl -XDELETE http://localhost:8888/ambassador/mapping/<mapping-name>/module/<module-name>

to delete a single module's config for a given mapping.

Also, the mapping-name identifies the mapping in statistics output and such.

Resources

To Ambassador, a resource is a group of one or more URLs that all share a common prefix in the URL path. For example:

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

all share the /resource1/ path prefix, so can be considered a single resource. On the other hand:

https://ambassador.example.com/resource1/foo
https://ambassador.example.com/resource2/bar
https://ambassador.example.com/resource3/baz/zing
https://ambassador.example.com/resource4/baz/zung

share only the prefix / -- you could tell Ambassador to treat them as a single resource, but it's probably not terribly useful.

Note that the length of the prefix doesn't matter: if you want to use prefixes like /v1/this/is/my/very/long/resource/name/, go right ahead, Ambassador can handle it.

Also note that Ambassador 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:

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

which is probably not what was intended.

Services

A service is exactly the same thing to Ambassador as it is to Kubernetes. When you tell Ambassador to map a resource to a service, it requires there to be a Kubernetes service with exactly the same name, and it trusts whatever Kubernetes has to say about ports and such.

At present, Ambassador relies on Kubernetes to do load balancing: it trusts that using the DNS to look up the service by name will do the right thing in terms of spreading the load across all instances of the service. This will change shortly, in order to gain better control of load balancing.

Rewrite Rules

Once Ambassador uses a prefix to identify the service to which a given request should be passed, it can rewrite the URL before handing it off to the service. By default, the prefix is rewritten to /, so e.g. if we map /prefix1/ to the service service1, then

http://ambassador.example.com/prefix1/foo/bar

would effectively be written to

http://service1/foo/bar

when it was handed to service1.

You can change the rewriting: for example, if you choose to rewrite the prefix as /v1/ in this example, the final target would be

http://service1/v1/foo/bar

And, of course, you can choose to rewrite the prefix to the prefix itself, so that

http://ambassador.example.com/prefix1/foo/bar

would be "rewritten" as

http://service1/prefix1/foo/bar

Modules

Modules let you enable and configure special behaviors for Ambassador, in ways that may apply to Ambassador as a whole or which may apply only to some mappings. The actual configuration possible for a given module depends on the module: at present, the only supported modules are the authentication module and the gRPC module.

You use PUT requests to the admin interface to save or update a module's global configuration:

curl -XPUT -H "Content-Type: application/json" -d <module-dict> \
      http://localhost:8888/ambassador/module/<module-name>

where <module-name> is the name of the module from the list below, and <module-dict> is a dictionary of configuration information. Which information is needed depends on the module.

Module configuration information can also be associated with mappings and consumers. These are also be set and updated using PUT requests:

curl -XPUT -H "Content-Type: application/json" -d <module-dict> \
      http://localhost:8888/ambassador/mapping/<mapping-name>/module/<module-name>

and

curl -XPUT -H "Content-Type: application/json" -d <module-dict> \
      http://localhost:8888/ambassador/consumer/<consumer-id>/module/<module-name>

You can get a list of all the modules for which Ambassador knows about configuration information with GET requests:

curl http://localhost:8888/ambassador/module

for global configuration, and

curl http://localhost:8888/ambassador/mapping/<mapping-name>/module

or

curl http://localhost:8888/ambassador/consumer/<consumer-id>/module

for mapping- or consumer-specific configuration.

Finally, you can delete module configuration with DELETE requests:

curl -XDELETE http://localhost:8888/ambassador/module/<module-name>
curl -XDELETE http://localhost:8888/ambassador/mapping/<mapping-name>/module/<module-name>
curl -XDELETE http://localhost:8888/ambassador/consumer/<consumer-id>/module/<module-name>

Consumers

Consumers represent human end users of Ambassador, and may be required for some modules to function. For example, the authentication module may require defining consumers to let Ambassador know who's allowed to authenticate.

A consumer is created with a POST request:

curl -XPOST -H"Content-Type: application/json" \
     -d<consumer-dict> \
     http://localhost:8888/ambassador/consumer

where consumer-dict has the details of the new consumer:

{
    "username": <username>,
    "fullname": <full-name>,
    "shortname": <short-name>,
    "modules": <module-dict>
}
  • username is the username to use when logging in, etc.
  • full-name is the consumer's full name. Ambassador assumes nothing about how full names are formed.
  • short-name (optional) is a short name that the consumer prefers to be called.
  • module-dict (optional) defines module configuration for this consumer.

You can get a list of all the consumers that Ambassador knows about with

curl http://localhost:8888/ambassador/consumer

and you can delete a specific consumer with

curl -XDELETE http://localhost:8888/ambassador/consumer/<consumer-id>

You can manipulate specific bits of module information for this consumer, as well (the modules section has more on this):

curl http://localhost:8888/ambassador/consumer/<consumer-id>/module/<module-name>

to read a single module's config;

curl -XPUT -H "Content-Type: application/json" \
     -d <module-dict> \
     http://localhost:8888/ambassador/consumer/<consumer-id>/module/<module-name>

to alter a single module's config (<module-dict> is the dictionary of new configuration information for the given consumer and module); and

curl -XDELETE http://localhost:8888/ambassador/consumer/<consumer-id>/module/<module-name>

to delete a single module's config for a given consumer.

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