Overview

This interface layer handles the communication with Etcd via the etcd-proxy interface.

Usage

Requires

This interface layer will set the following states, as appropriate:

• {relation_name}.connected The relation is established, but Etcd may not yet have provided any connection or service information.

• {relation_name}.available Etcd has provided its cluster string information, and is ready to handle incoming connections. The provided information can be accessed via the following methods:

  • cluster_string()

• {relation_name}.tls.available Etcd has provided client connection credentials for TLS communication.

  • client_ca - CA certificate
  • client_cert - Client Cert
  • client_key - Client Key

For example, a common application for this is configuring an applications backend kv storage, like Docker.

@when('proxy.available')
def prepare_etcd_proxy(proxy):
    con_string = proxy.cluster_string()
    # Save certificates to disk
    proxy.save_client_credentials('/etc/ssl/etcd')
    opts = {}
    opts['cluster_string'] = con_string
    opts['client_ca'] = '/etc/ssl/etcd/client-ca.pem'
    opts['client_cert'] = '/etc/ssl/etcd/client-cert.pem'
    opts['client_key'] = '/etc/ssl/etcd/client-key.pem'
    render('proxy_systemd_template', '/etc/systemd/system/etcd-proxy.service', opts)

Provides

A charm providing this interface is providing the Etcd cluster management connection string. This is similar to what ETCD requires when peering, declared as:

etcd0=https://192.168.1.2:2380,etcd1=https://192.168.2.22:2380

This interface layer will set the following states, as appropriate:

• {relation_name}.connected One or more clients of any type have been related. The charm should call the following methods to provide the appropriate information to the clients:

  • {relation_name}.provide_cluster_string()

• Additionally to secure the Etcd network connections, All of the client certificate keys must be set, which is conveniently enabled as a method on the interface:

Example:

@when('proxy.connected')
def send_cluster_details(proxy):
    bag = EtcdDatabag()
    # Read the client credentials
    ca = read_file_contents('/etc/ssl/etcd/ca.pem')
    cert = read_file_contents('/etc/ssl/etcd/client-cert.pem')
    key = read_file_contents('/etc/ssl/etcd/client-key.pem')
    # Set the cluster string for bootstrap
    proxy.set_cluster_string(bag.cluster_string())
    # Set the client credentials
    proxy.set_client_credentials(key, cert, ca)

def read_file_contents(filepath):
    with open(filepath, 'r') as fp:
        return fp.read(filepath)

Contact Information

Maintainer

• Charles Butler <charles.butler@canonical.com>

Contributors

• Mathew Bruzek <mathew.bruzek@canonical.com>

Etcd

• Etcd home page
• Etcd bug trackers
• Etcd Juju Charm