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flexnbd: Split the proxy mode out into its own binary.

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"flexnbd-proxy ..." should be identical in operation to "flexnbd proxy ..."
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nick
2013-03-19 13:13:37 +00:00
parent 21ac3cd0ed
commit 5257e93cb7
13 changed files with 411 additions and 281 deletions
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83
README.txt
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@@ -85,55 +85,6 @@ Options
^^^^^^^
As for 'serve'.
proxy
~~~~~
$ flexnbd proxy --addr <ADDR> --port <PORT>
--conn-addr <ADDR> --conn-port <PORT> [--bind <ADDR>] [global option]*
Proxy requests from an NBD client to an NBD server, resiliently. Only one
client can be connected (to the address specified by --addr and --port) at a
time, and ACLs cannot be applied to the client, as they can be to clients
connecting directly to a flexnbd in serve mode.
On starting up, the proxy will attempt to connect to the server specified by
--conn-addr and --conn-port (from the address specified by --bind, if given). If
it fails, then the process will die with an error exit status.
Assuming a successful connection to the `upstream` server is made, the proxy
will then start listening on the address specified by --addr and --port, waiting
for `downstream` to connect to it (this will be your NBD client). The client
will be given the same hello message as the proxy was given by the server.
When connected, any request the client makes will be read by the proxy and sent
to the server. If the server goes away for any reason, the proxy will remember
the request and regularly (~ every 5 seconds) try to reconnect to the server.
Upon reconnection, the request is sent and a reply is waited for. When a reply
is received, it is sent back to the client.
When the client disconnects, cleanly or otherwise, the proxy goes back to
waiting for a new client to connect. The connection to the server is maintained
at that point, in case it is needed again.
Only one request may be in-flight at a time under the current architecture; that
doesn't seem to slow things down much relative to alternative options, but may
be changed in the future if it becomes an issue.
Options
^^^^^^^
*--addr, -l ADDR*:
The address to listen on. Required.
*--port, -p PORT*:
The port to listen on. Required.
*--conn-addr, -C ADDR*:
The address of the NBD server to connect to. Required.
*--conn-port, -P PORT*:
The port of the NBD server to connect to. Required.
mirror
~~~~~~
@@ -415,40 +366,6 @@ Note that because the file is so small in this case, we see the source
server quit soon after we start the migration, and the destination
exited at roughly the same time.
Proxying
~~~~~~~~
The main point of the proxy mode is to allow clients that would otherwise break
when the NBD server goes away (during a migration, for instance) to see a
persistent TCP connection throughout the process, instead of needing its own
reconnection logic.
For maximum reliability, the proxy process would be run on the same machine as
the actual NBD client; an example might look like:
nbd-server-1$ flexnbd serve -l 10.0.0.1 -p 4777 myfile [...]
nbd-client-1$ flexnbd proxy -l 127.0.0.1 -p 4777 -C 10.0.0.1 -P 4777
nbd-client-1$ nbd-client -c 127.0.0.1 4777 /dev/nbd0
nbd-server-2$ flexnbd listen -l 10.0.0.2 -p 4777 -f myfile [...]
nbd-server-1$ flexnbd mirror --addr 10.0.0.2 -p 4777 [...]
Upon completing the migration, the mirroring and listening flexnbd servers will
both exit. With the proxy mediating requests, this does not break the TCP
connection that nbd-client is holding open. If no requests are in-flight, it
will not notice anything at all; if requests are in-flight, then the reply will
take longer than usual to be returned.
When flexnbd is restarted in serve mode on the second server:
nbd-server-2$ flexnbd serve -l 10.0.0.1 -p 4777 -f myfile [...]
The proxy notices and reconnects, fulfiling any request it has in its buffer.
The data in myfile has been moved between physical servers without the nbd
client process having to be disturbed at all.
BUGS
----