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IT08971: INDEFINITE HTTP GET REQUEST RETRIES CAN OCCUR WHEN USING SERVICES WITH PERSISTENT CONNECTIONS

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • Affected are customers sending HTTP GET requests to the
    multiprotocol gateway, web service proxy or web application
    firewall service.
    
    With the present implementation, users may end up in a state
    with indefinite retries for HTTP GET requests as long as
    DataPower has at least one live persistent connection to the
    backend server. After timeout interval for active connection it
    will terminate the connection and retry using remaining
    persistent connections to the backend. (If a new connection is
    opened because of half-dead backend this can continue
    indefinitely or until the request is served).
    

Local fix

  • This behavior cannot be turned off however it can be mitigated.
    For some relief out of this, the admin can lower the Back
    Persistent Timeout and/or User Agent's default Timeout. This
    should result in less persistent connections to the backend and
    thus less possible timeout hops
    
    Dropping the backend persistent connections option is also a
    possible workaround, but the consequences should be weighed
    carefully before making this decision. Not using persistent
    connections comes with a performance penalty, but it very much
    depends on the size/type of the transferred data and the
    speed/ping of the network.
    
    SLM is also strongly encouraged to prevent the backend from
    getting more load than it can handle.
    

Problem summary

  • Affected are all customers using the Multi-Protocol Gateway,
    Web Service Proxy or Web Application Firewall with persistent
    connection to the backend side.
    
    In case the backend server stops responding to HTTP GET
    requests while there are already some established TCP
    connections from the time the server worked OK, DataPower will
    automatically retry those GET requests after a timeout period.
    This will be retried until there are no established connections
    to the server.
    
    During a high load window, these unwanted retries might
    eventually keep flooding an already congested backend,
    especially if it is still able to establish some new
    connections.
    

Problem conclusion

Temporary fix

Comments

APAR Information

  • APAR number

    IT08971

  • Reported component name

    DATAPOWER

  • Reported component ID

    DP1234567

  • Reported release

    600

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2015-05-18

  • Closed date

    2015-08-12

  • Last modified date

    2015-09-02

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    DATAPOWER

  • Fixed component ID

    DP1234567

Applicable component levels

  • R600 PSN

       UP

  • R601 PSN

       UP

  • R602 PSN

       UP

  • R700 PSN

       UP

  • R710 PSN

       UP

  • R720 PSN

       UP



Document information

More support for: IBM DataPower Gateways
General

Software version: 6.0.0

Reference #: IT08971

Modified date: 02 September 2015