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ZooKeeper was initially designed and implemented using the Java NIO package. Later on, we add added Netty feature to optionally take place of replace NIO, since Netty has better support for supports SSL. Thus, SSL is only supported on top of Netty communication, which means if you want to use SSL you have to enable the Netty feature. We will discuss how to do it in the following section.

SSL

It's been added in ZOOKEEPER-2125.

Client-Server Communication

The communication between a ZooKeeper client and a server has Netty and SSL support. Note that Netty needs to be enabled to use SSL.

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ZooKeeper client can use Netty by setting property: 

zookeeper.clientCnxnSocket="org.apache.zookeeper.ClientCnxnSocketNetty"

In order to do secure communication on client, set this property: 

zookeeper.client.secure=true

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Then set up keystore and truststore environment by setting the following properties:

zookeeper.ssl.keyStore.location="/path/to/your/keystore"
zookeeper.ssl.keyStore.password="keystore_password"
zookeeper.ssl.trustStore.location="/path/to/your/truststore"
zookeeper.ssl.trustStore.password="truststore_password"

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ZooKeeper server can use Netty by setting this property:

zookeeper.serverCnxnFactory="org.apache.zookeeper.server.NettyServerCnxnFactory"

ZooKeeper server also needs to provide a listening port to accept secure client connections. This port is different from and running in parallel with the known “clientPort”. It should be added in “zoo.cfg”:

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secureClientPort=2281

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An example setup for running bin/zkServer.sh:

export SERVER_JVMFLAGS="
-Dzookeeper.serverCnxnFactory=org.apache.zookeeper.server.NettyServerCnxnFactory
-Dzookeeper.ssl.keyStore.location=/root/zookeeper/ssl/testKeyStore.jks 
-Dzookeeper.ssl.keyStore.password=testpass 
-Dzookeeper.ssl.trustStore.location=/root/zookeeper/ssl/testTrustStore.jks 
-Dzookeeper.ssl.trustStore.password=testpass" 

and set additionally in “zoo.cfg”:

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 secureClientPort=2281

For bin/zkCli.sh: 

export CLIENT_JVMFLAGS="
-Dzookeeper.clientCnxnSocket=org.apache.zookeeper.ClientCnxnSocketNetty 
-Dzookeeper.client.secure=true 
-Dzookeeper.ssl.keyStore.location=/root/zookeeper/ssl/testKeyStore.jks 
-Dzookeeper.ssl.keyStore.password=testpass 
-Dzookeeper.ssl.trustStore.location=/root/zookeeper/ssl/testTrustStore.jks 
-Dzookeeper.ssl.trustStore.password=testpass"

Start the ZK server, and then connect client to server’s port 2281 should work like normal.

Quorum

Not supported yet!There is currently no support for SSL for the communication between ZooKeeper servers.

Authentication

It's been added in ZOOKEEPER-2123.

When connecting to ZooKeeper via the secure port, the client is automatically authenticated with credentials associated with the client certificate. Specifically, the connection adds auth info with the scheme “x509” and the ACL ID set to the client certificate principal name.

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By default, authentication is performed by the X509AuthenticationProvider, corresponding to the auth scheme “x509.” This is initialized with server certificates and trusted client certificates specified according to the following properties: 

zookeeper.ssl.keyStore.location
zookeeper.ssl.keyStore.password
zookeeper.ssl.trustStore.location
zookeeper.ssl.trustStore.password

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Similar to the digest auth scheme, an x509 “superUser” can be configured by the server. Set the property zookeeper.X509AuthenticationProvider.superUser to an X500 Principal that corresponds to a client that should have full privileges to all znodes regardless of ACLs.

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To specify a custom authentication provider, extend the org.apache.zookeeper.server.auth.X509AuthenticationProvider. It may be necessary to extend javax.net.ssl.X509KeyManagerX509ExtendedKeyManager and javax.net.ssl.X509TrustManagerX509ExtendedTrustManager to get the desired behavior from the SSL stack. Then override X509AuthenticationProvider.getKeyManager() and getTrustManager() so that the SSLEngine will pick up the custom implementation.

To configure the ZooKeeper server to use the custom provider for authentication, choose a scheme name and set the property zookeeper.authProvider.[scheme] to the fully-qualified class name of the custom implementation. This will load the provider into the ProviderRegistry. Then set the property zookeeper.ssl.authProvider=[scheme] and that provider will be used for secure authentication.

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