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}.set_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:

from charmhelpers.core import hookenv
# this module lives in the etcd charm in lib/etcdctl.py
import etcdctl

@when('proxy.connected')
def send_cluster_details(proxy):
    # ETCD charm provides client keys via leader_data
    cert = hookenv.leader_get('client_certificate')
    key = hookenv.leader_get('client_key')
    ca = hookenv.leader_get('certificate_authority')
    # set the certificates on the conversation
    proxy.set_client_credentials(key, cert, ca)

    # format a list of cluster participants
    etcdctl = etcdctl.EtcdCtl()
    peers = etcdctl.member_list()
    cluster = []
    for peer in peers:
        # Potential member doing registration. Default to skip
        if 'peer_urls' not in peer.keys() or not peer['peer_urls']:
            continue
        peer_string = "{}={}".format(peer['name'], peer['peer_urls'])
        cluster.append(peer_string)
    # set the cluster string on the conversation
    proxy.set_cluster_string(','.join(cluster))

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