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Static Failover

Overview

In static failover a client is configured to use a failover IRU that lists the URIs of the broker connections the client can use. When establishing a connection, the client randomly chooses a URI from the list and attempts to establish a connection to it. If the connection does not succeed, the client chooses a new URI from the list and tries again. The client will continue cycling through the list until a connection attempt succeeds.

If a client's connection to a broker fails after it has been established, the client will attempt to reconnect to a different broker in the list. Once a connection to a new broker is established, the client will continue to use the new broker until the connection to the new broker is severed.

Failover URI

A failover URI is a composite URI that uses one of the following syntaxes:

  • failover://uri1,...,uriN
  • failover://(uri1,...,uriN)?TransportOptions

The URI list(uri1,...,uriN) is a comma-separated list containing the list of broker endpoint URIs to which the client can connect. The transport options(?TransportOptions) specified in the form of a query list, allow you to configure some of the failoiver behaviors.

Transport options

The failover protocol supports the transport options described in Table 1.

Table 1. Failover Transport Options

OptionDefaultDescription
initialReconnectDelay 10Specifies the number of milliseconds to wait before the first reconnect attempt.
maxReconnectDelay 30000Specifies the maximum amount of time, in milliseconds, to wait between reconnect attempts.
useExponentialBackOff trueSpecifies whether to use an exponential back-off between reconnect attempts.
backOffMultiplier 2Specifies the exponent used in the exponential back-off algorithm.
maxReconnectAttempts -1Specifies the maximum number of reconnect attempts before an error is returned to the client. -1 specifies unlimited attempts. 0 specifies that an initial connection attempt is made at start-up, but no attempts to failover over to a secondary broker will be made.
startupMaxReconnectAttempts 0Specifies the maximum number of reconnect attempts before an error is returned to the client on the first attempt by the client to start a connection. 0 specifies unlimited attempts.
randomize trueSpecifies if a URI is chosen at random from the list. Otherwise, the list is traversed from left to right.
backup falseSpecifies if the protocol initializes and holds a second transport connection to enable fast failover.
timeout -1Specifies the amount of time, in milliseconds, to wait before sending an error if a new connection is not established. -1 specifies an infinite timeout value.
trackMessages falseSpecifies if the protocol keeps a cache of in-flight messages that are flushed to a broker on reconnect.
maxCacheSize 131072Specifies the size, in bytes, used for the cache used to track messages.
updateURIsSupported trueSpecifies whether the client accepts updates to its list of known URIs from the connected broker. Setting this to false inhibits the client's ability to use dynamic failover. See ????.

Example

Example 1 shows a failover URI that can connect to one of two message brokers.

Example 1. Simple Failover URI

failover://(tcp://localhost:61616,tcp://remotehost:61616)?initialReconnectDelay=100

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