The on demand router (ODR) is an intelligent HTTP and Session
Initiation Protocol (SIP) proxy server in Intelligent Management. The ODR is the point
of entry into an Intelligent Management environment
and is a gateway through which HTTP requests and Session Initiation
Protocol (SIP) messages flow to back-end application servers. You
can configure the ODR to determine how it handles failure scenarios
and how it tunes certain work requests.
Before you begin
SIP is not supported on the z/OS® operating system.
Avoid trouble: The SIP ODR is stabilized, and is currently not recommended.
Use the SIP proxy server instead.
Restriction: Intelligent Management requires that all
configurations support User Datagram Protocol (UDP) traffic. However, Sysplex Distributor does not
support UDP traffic in all configurations. When you use Sysplex Distributor for a mobile deployment
manager in a configuration that includes Intelligent Management, the TCP/IP stack of the deployment
manager must own Sysplex Distributor. This setup allows UDP traffic to flow and Intelligent
Management to work properly. You can change the ownership of Sysplex Distributor by issuing a
VARY TCPIP,,SYSPLEX,DEACTIVATE
command.
We
now support a subset of ODR functions in an Apache or IBM HTTP web
server plug-in. Read about Intelligent Management for
web servers for more information.
About this task
The ODR can momentarily queue requests for less important
applications to allow requests from more important applications to
be handled more quickly or to protect back-end application servers
from being overloaded. The ODR is aware of the current location of
a dynamic cluster instance so that requests can be routed to the correct
endpoint. The ODR can also dynamically adjust the amount of traffic
that is sent to each individual server instance based on process utilization
and response times. The ODR performs WLOR (Weighted Least Outstanding
Request) load balancing for selecting a server within a cluster when
there is no affinity or when affinity is broken.
By default,
the ODR binds to ports 80 and 443 for listening on HTTP and HTTPS,
which requires running the ODR as a root user. If you want to run
the ODR as a non-root user, you must change the PROXY listening ports
to values greater than 1024.
The ODR is fully aware of the dynamic
state of the cell, so that if one server in the cell fails, the requests
are routed to another server. When the ODR is notified that the application
has initialized on the restarted server, the ODR routes requests to
that server again.
The ODR does not route any requests to the
application on the application server until the application completes
starting or initializing. If the application is started on other application
servers, then the requests are routed to them. If the application
is not started on any other servers, then the ODR still does not route
to the starting-in-progress application server. Instead, a 503 message
is returned.
Procedure
- For more information about ODRs, read about creating ODRs.
An ODR is a proxy server with advanced capabilities that
are used to route work to server nodes. The configuration of the ODR
in the DMZ is not supported. To configure ODRs to perform an SSL offload,
read about configuring SSL offload for all HTTPS traffic. For
information about other custom properties, read about the on demand
router system and custom properties.
- Follow the WebSphere® Application
Server Network Deployment instructions
in the proxy server settings topic to configure ODRs. For more information
about Intelligent Management specific
fields, read about configuring ODRs.
Avoid trouble: In
the Intelligent Management administrative
console, use the following path to define the configuration of the
ODR: .
- By default, the ODR matches the incoming protocol to the
outgoing protocol. For inbound HTTP requests, the request is forwarded
over outbound HTTP. For inbound HTTPS, the request is forwarded over
outbound HTTPS. This default behavior can either be changed for all
HTTP and HTTPS traffic that is handled by the ODR, or on a per-Web
module basis. For more information, read about configuring the SSL
offload for all HTTPS traffic.
- You can use ODR custom properties to change the behavior
of your ODR. For example, you can change the error code that the ODR
returns when messages are rejected because of processor or memory
overload. For more information, read about the on demand router system
and custom properties.
- A web server should be configured as a trusted secure proxy
because a trusted security proxy is allowed to pass information such
as the virtual host name, or user identity to the ODR in private HTTP
headers. For more information, read about configuring a web server
as a trusted proxy server.
- Define routing policies for generic server clusters.
- Routing and service policies for SIP are defined at the
ODRs. For more information, read about defining a service policy.
- Optionally, create routing rules using scripting. For more
information, see Intelligent Management: rules for ODR routing policy administrative tasks and manageODR.py script.
What to do next
Configure the middleware servers and dynamic clusters for
your environment.