Sijie Guo created BOOKKEEPER-252:
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Summary: Hedwig: provide a subscription mode to kill other
subscription channel when hedwig client is used as a proxy-style server.
Key: BOOKKEEPER-252
URL: https://issues.apache.org/jira/browse/BOOKKEEPER-252
Project: Bookkeeper
Issue Type: New Feature
Affects Versions: 4.1.0
Reporter: Sijie Guo
Assignee: Sijie Guo
Fix For: 4.2.0
In some case, we need to hedwig-client as proxy server to provide messaging
service to other users.
client -> proxy server 1 -> hedwig
\> proxy server 2 />
when client would connect to either proxy server to receive messages, the proxy
server would setup subscription channel to hedwig server.
we just want client to be simple, so when the channel between client and proxy
server is broken, client will try to connect to proxy servers thru VIP. it
might connect to other proxy server. for example, first time client connects to
proxy server 1, but the client found the connection is broken, it connects to
proxy server 2. when proxy server 2 tried to setup subscription channel to
hedwig, hedwig found that this subscription has existed before occupied by
proxy server 1.
the panic here is that proxy server 1 only disconnect old subscription channel
only when it detected the channel between client and itself is broken. The
detection might be delayed due to several reasons. so it might increment the
latency that messages are pushed to real client.
so we try to introduce a subscription mode called CREATE_OR_ATTACH_OR_KILL mode.
when a subscriber use this subscription mode, it would kill old existed
subscription channel. when using this subscription mode, we would turn off
auto-reconnect functionality in hedwig client and just tell client about the
channel disconnected event so client could do its logic when channel is
detected.
in order to provide some admin tool for admin guys to debug/operate, we provide
ADMIN mode. if a subscriber attach to a subscription using ADMIN mode, its
subscription channel would never be killed, then it is safe to guarantee admin
operations.
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