[jboss-jira] [JBoss JIRA] Reopened: (JGRP-130) Problems with reincarnation

[Bela Ban (JIRA)]

     [ http://jira.jboss.com/jira/browse/JGRP-130?page=all ]

Bela Ban reopened JGRP-130:
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> Problems with reincarnation
> ---------------------------
>
>                 Key: JGRP-130
>                 URL: http://jira.jboss.com/jira/browse/JGRP-130
>             Project: JGroups
>          Issue Type: Feature Request
>    Affects Versions: 2.2.9
>            Reporter: Bela Ban
>         Assigned To: Bela Ban
>             Fix For: 2.6, 2.5.2
>
>         Attachments: tcp.xml
>
>
> Problems with reincarnation
> ===========================
> Author: Bela Ban
> Version: $Id$
> The identity of a JGroups member is always the IP address and a port. The port is usually chosen by the OS, unless
> bind_port is set (not set by default).
> Let's say a member's address is hostA:5000. When that member dies and is restarted, the OS will likely assign a
> higher port, say 5002. This depends on how many other processes requested a port in between the start and restart
> of the member.
> JGroups relies on the fact that the assignment of ports by the OS is always (not necessarily monotonically)
> *increasing* across a single machine. If this is not the case, then the following problems can occur:
> 1. Restart:
> When a member P crashes and then is restarted, if FD is used and P is restarted *before* it is excluded,
> then we have a new member *under the same old address* ! Since it lost all of its state (e.g. retransmission table),
> retransmission requests sent to the new P will fail.
> 2. Shunning:
> Regarding shunning: a member keeps its last N (default is 100) ports used, and makes sure it doesn't reuse one of
> those already-used ports when it is shunned. However, this is process-wide and *not* machine-wide, e.g. when we have
> processes P1 on A:5000 and P2 on A:5002 (on machine A), and both of them are shunned at the same time,
> when they rejoin, P1 does not use port 5000, but might use port 5002, and P2 doesn't use 5002, but might use 5000, so
> they could assume each other's identity !
> Both problems cannot be solved by remembering the last 100 ports: in case #1, this list is lost because we start a
> new process and in case #2, the list is process-wide, but not machine-wide.
> Again, these problems occur *only* when the OS reuses previously assigned ports.
> SOLUTION:
> A: Use temporary storage (per host) to store the last N addresses assigned on a given host. This makes sure we
> don't reuse previous addresses
> B: Use logical addresses, such as java.rmi.VMID or java.rmi.server.UID, which are unique over time for a given host.
> Then, it doesn't matter what ports we use because the ports are not used to determine a member's identity.
> The JIRA task for logical addresses is http://jira.jboss.com/jira/browse/JGRP-129. 

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