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Add ZooKeeper-based dynamic configuration system.
The dynamic configuration system has two components: the app, which
reads, and the writer script. The latter is meant for use by humans, and
converts a [live_config] section of the INI file into JSON for storage
in ZooKeeper. The app will read this data on startup and place a watch
on the node to be notified, by ZooKeeper, of changes. This means that
running the writer script with new data will automatically propagate the
changes to every app very quickly, without restart.

The writer script relies on a human-entered password to authenticate
with ZooKeeper. The reddit app uses a different set of credentials
(specified in the INI file) to obtain read-only access to the
configuration data.

Also adds a new "live_config" spec to reddit and plugins. This spec is
parsed at write-time only and the parsed values are stored as JSON in
ZooKeeper.
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spladug committed Aug 3, 2012
1 parent 2c5021b commit f495dad
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Showing 5 changed files with 194 additions and 1 deletion.
4 changes: 4 additions & 0 deletions r2/example.ini
Expand Up @@ -493,3 +493,7 @@ beaker.session_secret = somesecret
# execute malicious code after an exception is raised.
#set debug = false

# the following configuration section makes up the "live" config. if zookeeper
# is enabled, then this configuration will be found by the app in zookeeper. to
# write it to zookeeper, use the writer script: scripts/write_live_config.
[live_config]
33 changes: 32 additions & 1 deletion r2/r2/lib/app_globals.py
Expand Up @@ -21,6 +21,7 @@
###############################################################################

from __future__ import with_statement
import ConfigParser
from pylons import config
import pytz, os, logging, sys, socket, re, subprocess, random
import signal
Expand All @@ -43,6 +44,26 @@
from r2.lib.plugin import PluginLoader


LIVE_CONFIG_NODE = "/config/live"


def extract_live_config(config, plugins):
"""Gets live config out of INI file and validates it according to spec."""

# ConfigParser will include every value in DEFAULT (which paste abuses)
# if we do this the way we're supposed to. sorry for the horribleness.
live_config = config._sections["live_config"].copy()
del live_config["__name__"] # magic value used by ConfigParser

# parse the config data including specs from plugins
parsed = ConfigValueParser(live_config)
parsed.add_spec(Globals.live_config_spec)
for plugin in plugins:
parsed.add_spec(plugin.live_config)

return parsed


class Globals(object):
spec = {

Expand Down Expand Up @@ -156,6 +177,9 @@ class Globals(object):
},
}

live_config_spec = {
}

def __init__(self, global_conf, app_conf, paths, **extra):
"""
Globals acts as a container for objects available throughout
Expand Down Expand Up @@ -235,13 +259,20 @@ def setup(self):
self.cache_chains = {}

# for now, zookeeper will be an optional part of the stack.
# if it's not configured, we will grab the expected config from the
# [live_config] section of the ini file
zk_hosts = self.config.get("zookeeper_connection_string")
if zk_hosts:
from r2.lib.zookeeper import connect_to_zookeeper
from r2.lib.zookeeper import connect_to_zookeeper, LiveConfig
zk_username = self.config["zookeeper_username"]
zk_password = self.config["zookeeper_password"]
self.zookeeper = connect_to_zookeeper(zk_hosts, (zk_username,
zk_password))
self.live_config = LiveConfig(self.zookeeper, LIVE_CONFIG_NODE)
else:
parser = ConfigParser.RawConfigParser()
parser.read([self.config["__file__"]])
self.live_config = extract_live_config(parser, self.plugins)

self.lock_cache = CMemcache(self.lockcaches, num_clients=num_mc_clients)
self.make_lock = make_lock_factory(self.lock_cache)
Expand Down
1 change: 1 addition & 0 deletions r2/r2/lib/plugin.py
Expand Up @@ -29,6 +29,7 @@
class Plugin(object):
js = {}
config = {}
live_config = {}

@property
def path(self):
Expand Down
23 changes: 23 additions & 0 deletions r2/r2/lib/zookeeper.py
Expand Up @@ -20,6 +20,7 @@
# Inc. All Rights Reserved.
###############################################################################

import json
import functools

from kazoo.client import KazooClient
Expand All @@ -45,3 +46,25 @@ def connect_to_zookeeper(hostlist, credentials):
client.connect()
client.add_auth("digest", ":".join(credentials))
return client


class LiveConfig(object):
"""A read-only dictionary view of configuration retrieved from ZooKeeper.
The data will be parsed using the given configuration specs, exactly like
the ini file based configuration. When data is changed in ZooKeeper, the
data in this view will automatically update.
"""
def __init__(self, client, key):
self.data = {}

@client.DataWatch(key)
def watcher(data, stat):
self.data = json.loads(data)

def __getitem__(self, key):
return self.data[key]

def __repr__(self):
return "<LiveConfig %r>" % self.data
134 changes: 134 additions & 0 deletions scripts/write_live_config
@@ -0,0 +1,134 @@
#!/usr/bin/env python
# The contents of this file are subject to the Common Public Attribution
# License Version 1.0. (the "License"); you may not use this file except in
# compliance with the License. You may obtain a copy of the License at
# http://code.reddit.com/LICENSE. The License is based on the Mozilla Public
# License Version 1.1, but Sections 14 and 15 have been added to cover use of
# software over a computer network and provide for limited attribution for the
# Original Developer. In addition, Exhibit A has been modified to be consistent
# with Exhibit B.
#
# Software distributed under the License is distributed on an "AS IS" basis,
# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
# the specific language governing rights and limitations under the License.
#
# The Original Code is reddit.
#
# The Original Developer is the Initial Developer. The Initial Developer of
# the Original Code is reddit Inc.
#
# All portions of the code written by reddit are Copyright (c) 2006-2012 reddit
# Inc. All Rights Reserved.
###############################################################################
"""Read config from an INI file and put it in ZooKeeper for instant use."""

import os
import sys
import json
import getpass
import ConfigParser

import kazoo.client
from kazoo.security import make_acl, make_digest_acl

from r2.lib.zookeeper import connect_to_zookeeper
from r2.lib.app_globals import extract_live_config, LIVE_CONFIG_NODE
from r2.lib.configparse import ConfigValue
from r2.lib.plugin import PluginLoader


USERNAME = "live-config"


def write_config_to_zookeeper(node, username, password, config, live_config):
"""Write given configuration to ZooKeeper with correct security etc."""

# read the zk configuration from the app's config
zk_hostlist = config.get("DEFAULT", "zookeeper_connection_string")
app_username = config.get("DEFAULT", "zookeeper_username")
app_password = config.get("DEFAULT", "zookeeper_password")

# connect to zk!
client = connect_to_zookeeper(zk_hostlist, (username, password))

# ensure that the path leading up to the config node exists. if it doesn't,
# create it with ACLs such that new stuff can be added below it, but no one
# but we can delete nodes.
parent_path = os.path.dirname(node)
client.ensure_path(parent_path, acl=[
# only we can delete children
make_digest_acl(username, password, delete=True),

# anyone authenticated can read/list children/create children
make_acl("auth", "", read=True, create=True),
])

# create or update the config node ensuring that only we can write to it.
json_data = json.dumps(live_config)
try:
client.create(node, json_data, acl=[
make_digest_acl(username, password, read=True, write=True),
make_digest_acl(app_username, app_password, read=True),
])
except kazoo.exceptions.NodeExistsException:
client.set(node, json_data)


def confirm_config(live_config):
"""Display the parsed live config and confirm that we should continue."""

max_key_length = max(len(k) for k in live_config.iterkeys())

print "Parsed Config:"
for key, value in sorted(live_config.iteritems(), key=lambda t: t[0]):
print " ", key.ljust(max_key_length), "=", repr(value)

answer = raw_input("Continue? [y|N] ")
return answer.lower() == "y"


def main():
"""Get and validate input from the user via CLI then write to ZK."""

progname = os.path.basename(sys.argv[0])

try:
ini_file_name = sys.argv[1]
except IndexError:
print >> sys.stderr, "USAGE: %s INI" % progname
return 1

config = ConfigParser.RawConfigParser()
try:
with open(ini_file_name, "r") as ini_file:
config.readfp(ini_file)
except (IOError, ConfigParser.Error), e:
print >> sys.stderr, "%s: %s: %s" % (progname, ini_file_name, e)
return 1

try:
plugin_config = config.get("DEFAULT", "plugins")
plugin_names = ConfigValue.tuple(plugin_config)
plugins = PluginLoader(plugin_names)
live = extract_live_config(config, plugins)
except ValueError as e:
print >> sys.stderr, "%s: %s" % (progname, e)
return 1
else:
if not confirm_config(live):
print "Oh, well, never mind then. Bye :("
return 0

password = getpass.getpass("Password: ")

write_config_to_zookeeper(LIVE_CONFIG_NODE,
USERNAME, password,
config, live)

print "Succesfully updated live config!"

return 0


if __name__ == "__main__":
sys.exit(main())

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