Spark Structured Streaming Blue/Green Deployments

Question

We'd like to be able to deploy our Spark jobs such that there isn't any downtime in processing data during deployments (currently there's about a 2-3 minute window). In my mind, the easiest way to do this is to simulate the "blue/green deployment" philosophy, which is to spin up the new version of the Spark job, let it warm up, then shut down the old job. However, with structured streaming & checkpointing, we cannot do this because the new Spark job sees that the latest checkpoint file already exists (from the old job). I've attached a sample error below. Does anyone have any thoughts on a potential workaround?

I thought about copying over the existing checkpoint directory to another checkpoint directory for the newly created job - while that should work as a workaround (some data might get reprocessed, but our DB should deduplicate), this seems super hacky and something I'd rather not pursue.

Caused by: org.apache.hadoop.fs.FileAlreadyExistsException: rename destination /user/checkpoint/job/offsets/3472939 already exists
    at org.apache.hadoop.hdfs.server.namenode.FSDirRenameOp.validateOverwrite(FSDirRenameOp.java:520)
    at org.apache.hadoop.hdfs.server.namenode.FSDirRenameOp.unprotectedRenameTo(FSDirRenameOp.java:364)
    at org.apache.hadoop.hdfs.server.namenode.FSDirRenameOp.renameTo(FSDirRenameOp.java:282)
    at org.apache.hadoop.hdfs.server.namenode.FSDirRenameOp.renameToInt(FSDirRenameOp.java:247)
    at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.renameTo(FSNamesystem.java:3677)
    at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.rename2(NameNodeRpcServer.java:914)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.rename2(ClientNamenodeProtocolServerSideTranslatorPB.java:587)
    at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:616)
    at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:982)
    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2049)
    at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2045)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698)
    at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2045)

    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at org.apache.hadoop.ipc.RemoteException.instantiateException(RemoteException.java:106)
    at org.apache.hadoop.ipc.RemoteException.unwrapRemoteException(RemoteException.java:73)
    at org.apache.hadoop.hdfs.DFSClient.rename(DFSClient.java:1991)
    at org.apache.hadoop.fs.Hdfs.renameInternal(Hdfs.java:335)
    at org.apache.hadoop.fs.AbstractFileSystem.rename(AbstractFileSystem.java:678)
    at org.apache.hadoop.fs.FileContext.rename(FileContext.java:958)
    at org.apache.spark.sql.execution.streaming.HDFSMetadataLog$FileContextManager.rename(HDFSMetadataLog.scala:356)
    at org.apache.spark.sql.execution.streaming.HDFSMetadataLog.org$apache$spark$sql$execution$streaming$HDFSMetadataLog$$writeBatch(HDFSMetadataLog.scala:160)
    ... 20 more
Caused by: org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.fs.FileAlreadyExistsException): rename destination /user/checkpoint/job/offsets/3472939 already exists

Answer 1

It is possible, but it will add some complexity to your application. Starting streams is in general fast, so it is fair to assume, that delay is caused by initialization of static objects and dependencies. In that case you'll need only SparkContext / SparkSession, and no streaming dependencies so process can be described as:

• Start new Spark application.
• Initialize batch-oriented objects.
• Pass message to the previous application to step down.
• Wait for confirmation.
• Start streams.

At the very high level, the happy path could be visualized as:

Since it is very generic pattern it could be implemented in a different ways, depending on a language and infrastructure:

• Lightweight messaging queue like ØMQ.
• Passing messages through distributed file system.
• Placing applications in an interactive context (Apache Toree, Apache Livy) and using external client for orchestration.