patroni/helpers/etcd.py

import logging
import requests
import time

from collections import namedtuple
from helpers.errors import CurrentLeaderError, EtcdError

logger = logging.getLogger(__name__)


Member = namedtuple('Member', 'hostname,address,ttl')
Cluster = namedtuple('Cluster', 'leader,last_leader_operation,members')


class Etcd:

    def __init__(self, config):
        self.ttl = config['ttl']
        self.base_client_url = 'http://{host}/v2/keys/service/{scope}'.format(**config)
        self.postgres_cluster = None

    def get_client_path(self, path, max_attempts=1):
        attempts = 0
        response = None

        while True:
            ex = None
            try:
                response = requests.get(self.client_url(path))
                if response.status_code == 200:
                    break
            except Exception as e:
                logger.exception('get_client_path')
                ex = e

            attempts += 1
            if attempts < max_attempts:
                logger.info('Failed to return %s, trying again. (%s of %s)', path, attempts, max_attempts)
                time.sleep(3)
            elif ex:
                raise ex
            else:
                break

        return response.json(), response.status_code

    def put_client_path(self, path, **data):
        try:
            response = requests.put(self.client_url(path), data=data)
            return response.status_code in [200, 201]
        except:
            logger.exception('PUT %s data=%s', path, data)
            return False

    def delete_client_path(self, path):
        try:
            response = requests.delete(self.client_url(path))
            return response.status_code == 204
        except:
            logger.exception('DELETE %s', path)
            return False

    def client_url(self, path):
        return self.base_client_url + path

    @staticmethod
    def find_node(node, key):
        """
        >>> Etcd.find_node({}, None)
        >>> Etcd.find_node({'dir': True, 'nodes': [], 'key': '/test/'}, 'test')
        """
        if not node.get('dir', False):
            return None
        key = node['key'] + key
        for n in node['nodes']:
            if n['key'] == key:
                return n
        return None

    def get_cluster(self):
        try:
            response, status_code = self.get_client_path('?recursive=true')
            if status_code == 200:
                # get list of members
                node = self.find_node(response['node'], '/members') or {'nodes': []}
                members = [Member(n['key'].split('/')[-1], n['value'], n.get('ttl', None)) for n in node['nodes']]

                # get last leader operation
                last_leader_operation = 0
                node = self.find_node(response['node'], '/optime')
                if node:
                    node = self.find_node(node, '/leader')
                    if node:
                        last_leader_operation = int(node['value'])

                # get leader
                leader = None
                node = self.find_node(response['node'], '/leader')
                if node:
                    for m in members:
                        if m.hostname == node['value']:
                            leader = m
                            break
                    if not leader:
                        leader = Member(leader['value'], None, None)

                return Cluster(leader, last_leader_operation, members)
            elif status_code == 404:
                return Cluster(None, None, [])
        except:
            logger.exception('get_cluster')

        raise EtcdError('Etcd is not responding properly')

    def current_leader(self):
        try:
            cluster = self.get_cluster()
            if not cluster.leader or not cluster.leader.address:
                return None
            return cluster.leader
        except:
            raise CurrentLeaderError("Etcd is not responding properly")

    def touch_member(self, member, connection_string):
        return self.put_client_path('/members/' + member, value=connection_string, ttl=self.ttl)

    def take_leader(self, value):
        return self.put_client_path('/leader', value=value, ttl=self.ttl)

    def attempt_to_acquire_leader(self, value):
        ret = self.put_client_path('/leader', value=value, ttl=self.ttl, prevExist=False)
        ret or logger.info('Could not take out TTL lock')
        return ret

    def update_leader(self, state_handler):
        ret = self.put_client_path('/leader', value=state_handler.name, ttl=self.ttl, prevValue=state_handler.name)
        ret and self.put_client_path('/optime/leader', value=state_handler.last_operation())
        return ret

    def race(self, path, value):
        return self.put_client_path(path, value=value, prevExist=False)

    def delete_member(self, member):
        return self.delete_client_path('/members/' + member)

    def delete_leader(self, value):
        return self.delete_client_path('/leader?prevValue=' + value)