The Channel Interceptor object

Table of Contents

Introduction

Apache Tribes supports an interceptor architecture to intercept both messages and membership notifications. This architecture allows decoupling of logic and opens the way for some very useful feature add ons.

Available Interceptors

  • org.apache.catalina.tribes.group.interceptors.TcpFailureDetector
  • org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor
  • org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor
  • org.apache.catalina.tribes.group.interceptors.NonBlockingCoordinator
  • org.apache.catalina.tribes.group.interceptors.OrderInterceptor
  • org.apache.catalina.tribes.group.interceptors.SimpleCoordinator
  • org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor
  • org.apache.catalina.tribes.group.interceptors.TwoPhaseCommitInterceptor
  • org.apache.catalina.tribes.group.interceptors.DomainFilterInterceptor
  • org.apache.catalina.tribes.group.interceptors.FragmentationInterceptor
  • org.apache.catalina.tribes.group.interceptors.GzipInterceptor
  • org.apache.catalina.tribes.group.interceptors.TcpPingInterceptor
  • org.apache.catalina.tribes.group.interceptors.EncryptInterceptor

Static Membership

In addition to dynamic discovery, Apache Tribes also supports static membership, with membership verification. To achieve this add the org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor after the org.apache.catalina.tribes.group.interceptors.TcpFailureDetector interceptor. Inside the StaticMembershipInterceptor you can add the static members you wish to have. The TcpFailureDetector will do a health check on the static members,and also monitor them for crashes so they will have the same level of notification mechanism as the members that are automatically discovered.

     <Interceptor className="org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor">
       <LocalMember className="org.apache.catalina.tribes.membership.StaticMember"
                  domain="staging-cluster"
                  uniqueId="{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,1}"/>
       <Member className="org.apache.catalina.tribes.membership.StaticMember"
                  port="5678"
                  securePort="-1"
                  host="tomcat01.mydomain.com"
                  domain="staging-cluster"
                  uniqueId="{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}"/>
     </Interceptor>

Attributes

Common Attributes

Attribute Description
className Required, as there is no default
optionFlag If you want the interceptor to trigger on certain message depending on the message's option flag, you can setup the interceptors flag here. The default value is 0, meaning this interceptor will trigger on all messages.

org.apache.catalina.tribes.group.interceptors.DomainFilterInterceptor Attributes

Attribute Description
domain The logical cluster domain that this Interceptor accepts. Two different type of values are possible:
1. Regular string values like "staging-domain" or "tomcat-cluster" will be converted into bytes using ISO-8859-1 encoding.
2. byte array in string form, for example {216,123,12,3}
logInterval This value indicates the interval for logging for messages from different domains. The default is 100, which means that to log per 100 messages.

org.apache.catalina.tribes.group.interceptors.FragmentationInterceptor Attributes

Attribute Description
expire How long do we keep the fragments in memory and wait for the rest to arrive. The default is 60000 ms.
maxSize The maximum message size in bytes. If the message size exceeds this value, this interceptor fragments the message and sends them. If it is less than this value, this interceptor does not fragment the message and sent in as one message. The default is 1024*100.

org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor Attributes

Attribute Description
optionFlag The default and hard coded value is 8 (org.apache.catalina.tribes.Channel.SEND_OPTIONS_ASYNCHRONOUS). The dispatcher will trigger on this value only, as it is predefined by Tribes.
alwaysSend What behavior should be executed when the dispatch queue is full. If true (default), then the message is is sent synchronously, if false an error is thrown.
maxQueueSize Size in bytes of the dispatch queue, the default value is 1024*1024*64 (64MB) sets the maximum queue size for the dispatch queue if the queue fills up, one can trigger the behavior, if alwaysSend is set to true, the message will be sent synchronously if the flag is false, an error is thrown
maxThreads The maximum number of threads in this pool, default is 10.
maxSpareThreads The number of threads to keep in the pool, default is 2.
keepAliveTime Maximum number of milliseconds of until Idle thread terminates. Default value is 5000(5 seconds).

org.apache.catalina.tribes.group.interceptors.TcpFailureDetector Attributes

Attribute Description
connectTimeout Specifies the timeout, in milliseconds, to use when attempting a TCP connection to the suspect node. Default is 1000.
performSendTest If true is set, send a test message to the suspect node. Default is true.
performReadTest If true is set, read the response of the test message that sent. Default is false. Note: if performSendTest is false, this attribute will have no effect.
readTestTimeout Specifies the timeout, in milliseconds, to use when performing a read test to the suspicious node. Default is 5000.
removeSuspectsTimeout The maximum time(in seconds) for remove from removeSuspects. Member of removeSuspects will be automatically removed after removeSuspectsTimeout. If a negative value specified, the removeSuspects members never be removed until disappeared really. If the attribute is not provided, a default of 300 seconds (5 minutes) is used.

org.apache.catalina.tribes.group.interceptors.TcpPingInterceptor Attributes

Attribute Description
interval If useThread == true, defines the interval of sending a ping message. default is 1000 ms.
useThread Flag of whether to start a thread for sending a ping message. If set to true, this interceptor will start a local thread for sending a ping message. if set to false, channel heartbeat will send a ping message. default is false.

org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor Attributes

Attribute Description
interval Defines the interval in number of messages when we are to report the throughput statistics. The report is logged to the org.apache.juli.logging.LogFactory.getLog(ThroughputInterceptor.class) logger under the INFO level. Default value is to report every 10000 messages.

org.apache.catalina.tribes.group.interceptors.EncryptInterceptor Attributes

The EncryptInterceptor adds encryption to the channel messages carrying session data between nodes. Added in Tomcat 9.0.13.

If using the TcpFailureDetector, the EncryptInterceptor must be inserted into the interceptor chain before the TcpFailureDetector. This is because when validating cluster members, TcpFailureDetector writes channel data directly to the other members without using the remainder of the interceptor chain, but on the receiving side, the message still goes through the chain (in reverse). Because of this asymmetry, the EncryptInterceptor must execute before the TcpFailureDetector on the sender and after it on the receiver, otherwise message corruption will occur.

Attribute Description
encryptionAlgorithm The encryption algorithm to be used, including the mode and padding. Please see https://docs.oracle.com/javase/8/docs/technotes/guides/security/StandardNames.html for the standard JCA names that can be used. EncryptInterceptor currently supports the following block-cipher modes: CBC, OFB, CFB, and GCM. The length of the key will specify the flavor of the encryption algorithm to be used, if applicable (e.g. AES-128 versus AES-256). The default algorithm is AES/CBC/PKCS5Padding.
encryptionKey The key to be used with the encryption algorithm. The key should be specified as hex-encoded bytes of the appropriate length for the algorithm (e.g. 16 bytes / 32 characters / 128 bits for AES-128, 32 bytes / 64 characters / 256 bits for AES-256, etc.).

Nested Components

StaticMember Attributes

LocalMember:
Static member that is the local member of the static cluster group.

Attribute Description
className Only one implementation available:org.apache.catalina.tribes.membership.StaticMember
port There is no need to set. The value of this attribute inherits from the cluster receiver setting.
securePort There is no need to set. The value of this attribute inherits from the cluster receiver setting.
host There is no need to set. The value of this attribute inherits from the cluster receiver setting.
domain The logical cluster domain for that this static member listens for cluster messages. Two different type of values are possible:
1. Regular string values like "staging-domain" or "tomcat-cluster" will be converted into bytes using ISO-8859-1 encoding. 2. byte array in string form, for example {216,123,12,3}
uniqueId A universally uniqueId for this static member. The values must be 16 bytes in the following form:
1. byte array in string form, for example {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}

Member:
Static member that add to the static cluster group.

Attribute Description
className Only one implementation available:org.apache.catalina.tribes.membership.StaticMember
port The port that this static member listens to for cluster messages
securePort The secure port this static member listens to for encrypted cluster messages default value is -1, this value means the member is not listening on a secure port
host The host (or network interface) that this static member listens for cluster messages. Three different type of values are possible:
1. IP address in the form of "216.123.1.23"
2. Hostnames like "tomcat01.mydomain.com" or "tomcat01" as long as they resolve correctly
3. byte array in string form, for example {216,123,12,3}
domain The logical cluster domain for that this static member listens for cluster messages. Two different type of values are possible:
1. Regular string values like "staging-domain" or "tomcat-cluster" will be converted into bytes using ISO-8859-1 encoding.
2. byte array in string form, for example {216,123,12,3}
uniqueId A universally uniqueId for this static member. The values must be 16 bytes in the following form:
1. byte array in string form, for example {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}

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