Overview

This interface layer implements the basic form of the http interface protocol, which is used for things such as reverse-proxies, load-balanced servers, REST service discovery, et cetera.

Usage

Provides

By providing the http interface, your charm is providing an HTTP server that can be load-balanced, reverse-proxied, used as a REST endpoint, etc.

Your charm need only provide the port on which it is serving its content, as soon as the {relation_name}.available state is set:

@when('website.available')
def configure_website(website):
    website.configure(port=hookenv.config('port'))

Requires

By requiring the http interface, your charm is consuming one or more HTTP servers, as a REST endpoint, to load-balance a set of servers, etc.

Your charm should respond to the {relation_name}.available state, which indicates that there is at least one HTTP server connected.

The services() method returns a list of available HTTP services and their associated hosts and ports.

The return value is a list of dicts of the following form:

[
    {
        'service_name': name_of_service,
        'hosts': [
            {
                'hostname': address_of_host,
                'port': port_for_host,
            },
            # ...
        ],
    },
    # ...
]

A trivial example of handling this interface would be:

from charms.reactive.helpers import data_changed

@when('reverseproxy.available')
def update_reverse_proxy_config(reverseproxy):
    services = reverseproxy.services()
    if not data_changed('reverseproxy.services', services):
        return
    for service in services:
        for host in service['hosts']:
            hookenv.log('{} has a unit {}:{}'.format(
                services['service_name'],
                host['hostname'],
                host['port']))