NameNodeProxy

Another HDFS Federation solution from bytedance.

Features

NameNode RPC proxy instead of ViewFS, no client-side changes.
Multiple language client (i.e. snakebite) support.
Stateless. Easy to scale to multiple instances.
High throughput with little latency introduced.
Request throttle. Single NameNode malfunction will not affect globally.

Compared with ViewFS and WebHDFS:

	NNProxy	ViewFS	WebHDFS
Multiple language support	Yes	No	Yes
Unified APIs provided	Yes	Yes	No
Mount table stored in	Zookeeper	Configuration	Configuration
	* Client-side configurations are not usually easy to change
Client-side library	No	Heavy	Light
Call latency introduced	Medium	No latency	High
Centralized cache support	Yes	Yes	No

Benchmark

Benchmark result with NameNode Benchmark 0.4:

	Direct TPS	NNProxy TPS (3 proxy instances)
create_write @ 16maps	263,294	247,799
create_write @ 128maps	3,008,604	2,563,465
rename @ 128maps	474,671	471,240

(numOfFiles 512 each map, NameNode CPU: Xeon E5-2630 v2 * 2, network RTT 0.1ms)

Build

IMPORTANT: NNProxy works only with patched NameNode. See /hadoop-patches in git repository. These patches add proxy support to hadoop-common library. Each of them must be applied before compiling.

Build with maven:

$ cd nnproxy/hadoop-nnproxy
$ mvn package -DskipTests

Built jar are shaded with necessary libraries, which can run with hadoop jar.

Deploy

Organize working directory as follows:

bin/
bin/nnproxy
lib/
lib/hadoop-nnproxy-0.1.0.jar

Then run bin/nnproxy with configuration arguments to start proxy server. Note that before starting proxy server, a mount table must be deployed first.

For example:

# Setup zk environment, for simplicity, not necessary
export NNPROXY_ZK_QUORUM="127.0.0.1:2181"
export NNPROXY_MOUNT_TABLE_ZKPATH="/hadoop/hdfs/mounts"

export NNPROXY_OPTS="-Ddfs.nnproxy.mount-table.zk.quorum=$NNPROXY_ZK_QUORUM -Ddfs.nnproxy.mount-table.zk.path=$NNPROXY_MOUNT_TABLE_ZKPATH"

# Deploy mount table, example above mounts / to hdfs://toutiaonn0 and /data 
# to hdfs://toutiaonn1. In which case, accessing /data/recommend would be 
# transparently redirected to hdfs://toutiaonn1/data/recommend.
# In this example, toutiaonn0 and toutiaonn1 are fs names configured with 
# auto failover HA. Using ip:port directly (non-HA setup) are also fesible.
echo 'hdfs://toutiaonn0 /' > mounts
echo 'hdfs://toutiaonn1 /data' >> mounts
cat mounts | bin/nnproxy load $NNPROXY_OPTS

# Run proxy (remember these args)
bin/nnproxy proxy $NNPROXY_OPTS

Look into class com.bytedance.hadoop.hdfs.ProxyConfig for more configurations available.

Proxy server metrics are also available with hadoop-metrics2.

Mount table management

Once proxy server is started, it watches mount table node on ZooKeeper for further changes.

Run bin/nnproxy dump $NNPROXY_OPTS to dump current mount table to stdout.

Run bin/nnproxy load $NNPROXY_OPTS to load mount table from stdin.

One can also alter data stored in mount table ZK node directly (or possibly build APIs or UIs). All these changes take effect immediately.

Mount table are delimited text with 3 columns: targetFS, path and attributes, in that order. For example:

hdfs://toutiaonn0   /        none
hdfs://toutiaonn1   /data    none

Each row advises proxy to redirect path and its children to specified targetFS. attributes are currently reserved and is of no use.

Future work

Support readonly attribute in mounts
More kind of operations through proxy

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.