public class UpdateForwardingStockQuotes extends RouterDrivenStockQuotes
RouterDrivenStockQuotes
and illustrates use
of an HA unaware router (implemented by SimpleRouter
), that load
balances requests (both read and write) across all the nodes in a
replication group. This example is meant to illustrate how a load balancer
appliance might fit into the JE HA architecture, where SimpleRouter
plays the role of the load balancer appliance for purposes of the example.
Be sure to read the Example Overview
first to put this
example into context.
The router is unaware of the state (Master or Replica) of each node, or the
type (read or write) of the request. Nodes use the StateChangeListener
to track the
node that is currently the master and redirect write requests to it. That
is, unlike the RouterDrivenStockQuotes
example, it's the nodes and
not the router that keeps track of the current master.
In this example, unlike StockQuotes
, only the
SimpleRouter
has a console associated with it. It accepts commands
typed into its console and forwards them as appropriate to the nodes in the
group. The logic for tracking the Master resides in each node, and is
supplied by the StateChangeListener
.
Each node, which in this example is an instance of
UpdateForwardingStockQuotes
, establishes a server socket on
which it can listen for requests from SimpleRouter
. Read
requests are processed directly by the node. Write requests are redirected
to the current master and the result is communicated back to
SimpleRouter
.
The request flow between nodes in this example is shown below.
---------------- Read and Write requests | SimpleRouter |------------------------------------|| | Instance |---------------------|| || ---------------- || || || || || || \/ || || ------------------------------- || || | UpdateForwardingStockQuotes | || || | Instance 1: Master | || || ------------------------------- \/ || /\ ------------------------------- || || | UpdateForwardingStockQuotes | || ||---------- | Instance 2: Replica | || || Write ------------------------------- \/ || requests ------------------------------- || | UpdateForwardingStockQuotes | ||--------------------------| Instance 3: Replica | ------------------------------- ...more Replica instances...
This example is intended to be illustrative. It forwards requests as text, and receives responses in text form. Actual applications may for example, forward HTTP requests, or use some other application level network protocol to forward such requests.
Please review the javadoc in StockQuotes
for a detailed description
of the arguments that must be supplied at startup. The only difference is
that you must use the name of this class when invoking the java vm.
For example, the first node can be started as follows:
java je.rep.quote.UpdateForwardingStockQuotes -env /tmp/stockQuotes1 \ -nodeName n1 \ -nodeHost node.acme.com:5001 \ -helperHost node.acme.com:5001
This instance of the application will therefore use port 5001 for HA, and,
by convention, port 5101 (5001 + HARouter.APP_PORT_DISPLACEMENT
)
for application messages sent to it.
In addition to starting the nodes, you will also need to start the
SimpleRouter
as described in its javadoc.
SimpleRouter
Modifier and Type | Method and Description |
---|---|
static void |
main(java.lang.String[] argv) |
quit
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