apps are not like shipped software • You only have one user (you), so usually only a single copy of your code is in use at a time. • except when you’re deploying • branch management doesn’t apply Saturday, November 10, 12
a feature long before you launch it and nobody will know” • “You can completely rewrite your infrastructure and keep the UI the same and nobody will know” “Idea one: separate feature launches from infrastructure launches” Saturday, November 10, 12
backend systems and keep the UI the same and nobody will know” • “You can deploy a non-user facing change to only a small percentage of servers and nobody will know” “Idea two: run multiple versions of your code at once” Saturday, November 10, 12
to your app in real time • It manages different types of environments – staging, production, development • It can also manage config on a host-by-host basis Saturday, November 10, 12
representing the path to the znode you wish to access >>> zookeeper.get( ... '/services/pycon/conf')[0] '{ "locale": "Canada", "times_talk_given": 0, "is_awesome": true }' Saturday, November 10, 12
be notified if the znode ever changes >>> def cb(data, stat): ... print "I changed. New value: ", data ... >>> kc.create('/test', 'foobar') u'/test' >>> kc.get('/test', watch=cb) ('foobar', ...) >>> kc.set('/test', 'baz') I changed. New value: baz Saturday, November 10, 12
supports MVCC • Multiversion concurrency control • a way of enforcing consistency • ensures multiple writers don’t clobber each other Saturday, November 10, 12
>>> # stat holds metadata about the znode >>> config, stat = zk.get('/test') >>> # let's look at the current version >>> stat.version 1 >>> # try updating the znode with the current version >>> zk.set('/test', 'foobar', version=stat.version) >>> # success >>> zk.get('/test')[0] 'foobar' >>> # we can also choose to overwrite any value >>> zk.set('/test', 'baz', version=-1) >>> zk.get('/test')[0] 'baz' >>> # let's see what happens if we pass a wrong version >>> zk.set('/test', 'foobaz', version=9000) >>> # we get an exception because version must be the >>> # current version of the znode you're trying to change kazoo.exceptions.BadVersionError: ((), {}) Saturday, November 10, 12
for a percentage of users if jones.get('pct_new_queue', 0) > random(): queue = new_queue # enable features by user bucket buckets = jones['macguffin_buckets'] if (user.id % bucket) in jones['macguffin_enabled_for']: user.wants_macguffin = True Saturday, November 10, 12
Clients MUST only talk to ZooKeeper • Accessing configuration MUST be simple (i.e. no computation) • Unique views of the config MUST be available on a host- by-host basis Saturday, November 10, 12
optional ZK ACLs to ensure consistency • Jones class deals with complexities of materializing views and managing associations. Saturday, November 10, 12
on nodemaps and environment view • nodemaps watch makes sure we always know what environment is ours • view watch keeps config dict up to date. Can optionally invoke callback • Simple! Saturday, November 10, 12
set some root config • show that we can get value from client • change config. show that it reflects in client • add child env. associate to my laptop • show that config changes & inheritance works Saturday, November 10, 12
• provides a hierarchy of configurations, with children inheriting from parents • a web UI for managing config as a JSON object • a way to peg certain configurations to specific hosts/ processes/clusters/etc. Saturday, November 10, 12
Web App auth/ACLs for compartmentalization • Audit log • Ability to peg to versions • i.e. this service always needs version N • see github issues Saturday, November 10, 12
going to perform this bit of work? zk = KazooClient() election = zk.Election( "/election2012", "obama-biden" ) # blocks until the election is won, then calls # swear_in() election.run(swear_in) Saturday, November 10, 12
a monotonically increasing counter to the end of path. • e.g. 2 calls to create sequence znodes at /lock- will result in • /lock-0 • /lock-1 • sequences are unique to the parent Saturday, November 10, 12
quorum) of nodes before success is communicated • some nodes may have old data • Reads happen from any node • Writes are forwarded through master • As ensemble size grows, read performance increases while write performance decreases. Saturday, November 10, 12
are correct (i.e., with 2f + 1 server we can tolerate f failures).[5] • Means we need to run an odd number of server • 3 is the minimum, 5 is recommended • with 5 we can tolerate 2 failures Saturday, November 10, 12
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