syncthing-monitor/syncthing_monitor/etcd_client.py

import json

import etcd3 as etcd3
from retrying import retry

CLUSTER_INFO_KEY = '/syncthing_monitor/cluster_info'


class EtcdClient:
    def __init__(self, host, port, key=CLUSTER_INFO_KEY):
        self.etcd = etcd3.client(host=host, port=port)
        self.key = key

    @retry(stop_max_delay=60000, wait_fixed=500)
    def load_cluster_info(self):
        print("Retrieving cluster info from etcd...", flush=True)
        raw_value = self.etcd.get(self.key)[0]
        if raw_value is None:
            return {'devices': []}
        return json.loads(raw_value)

    def add_device_to_cluster(self, device_id, node_name, address):
        with self.etcd.lock('syncthing_monitor'):
            cluster_info = self.load_cluster_info()

            print("Checking for existing device with node name '{0}'...".format(node_name), flush=True)
            existing_device = next(
                (device for device in cluster_info['devices'] if node_name in device['node_name']),
                None)

            if existing_device is not None:
                self.update_existing_device(cluster_info, existing_device, device_id, node_name, address)
                return

            print(
                "Existing device not found; Creating new cluster_info entry for node name: '{0}'...".format(node_name),
                flush=True)

            new_device = {
                'id': device_id,
                'node_name': node_name,
                'address': address
            }

            cluster_info['devices'].append(new_device)

            self.do_cluster_info_update(cluster_info)

    def update_existing_device(self, cluster_info, existing_device, device_id, node_name, address):

        if device_id == existing_device['id']:
            print("Existing device contains up-to-date ID!  No need to update.".format(node_name), flush=True)
            return

        print("Existing device with my node name '{0}' contains stale info!  Updating...".format(node_name), flush=True)
        existing_device['id'] = device_id
        existing_device['address'] = address

        self.do_cluster_info_update(cluster_info)

    @retry(stop_max_delay=60000, wait_fixed=500)
    def do_cluster_info_update(self, cluster_info):
        print("Updating etcd value for '{0}': {1}".format(self.key, json.dumps(cluster_info)), flush=True)
        self.etcd.put(self.key, json.dumps(cluster_info))

    def get_device_list(self):
        device_list = self.load_cluster_info()['devices']
        print("Obtained device_list devices from etcd: {0}".format(json.dumps(device_list)), flush=True)
        return device_list

    def register_device_update_handler(self, device_update_handler):
        self.etcd.add_watch_callback(self.key, device_update_handler)