2016-11-27 15:32:05 +00:00
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Parallelization
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===============
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Description
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-----------
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cdist has two modes of parallel operation.
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One of them is to operate on each host in separate process. This is enabled
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with :strong:`-p/--parallel` option.
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The other way is to operate in parallel within one host where you specify
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the number of jobs. This is enabled with :strong:`-j/--jobs` option where you
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can specify the number of parallel jobs. By default,
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2017-06-13 20:57:11 +00:00
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:strong:`multiprocessing.cpu_count()` is used. For this mode global explorers,
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object preparation and object run are supported and this option is still in
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:strong:`beta`.
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2016-11-27 15:32:05 +00:00
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You can, of course, use those two options together. This means that each host
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will be processed by its own process. Within each process cdist will operate
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using specified number of parallel jobs.
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For more info on those options see :strong:`cdist`\ (1).
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Examples
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--------
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.. code-block:: sh
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# Configure hosts read from file hosts.file in parallel
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$ cdist config -p -f hosts.file
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# Configure hosts read from file hosts.file sequentially but using default
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# number of parallel jobs
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$ cdist config -b -j -f hosts.file
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# Configure hosts read from file hosts.file in parallel using 16
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# parallel jobs
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$ cdist config -b -j 16 -p -f hosts.file
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Caveats
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-------
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When operating in parallel, either by operating in parallel for each host
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(-p/--parallel) or by parallel jobs within a host (-j/--jobs), and depending
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on target SSH server and its configuration you may encounter connection drops.
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This is controlled with sshd :strong:MaxStartups configuration options.
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You may also encounter session open refusal. This happens with ssh multiplexing
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when you reach maximum number of open sessions permitted per network
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connection. In this case ssh will disable multiplexing.
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This limit is controlled with sshd :strong:MaxSessions configuration
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options. For more details refer to :strong:`sshd_config`\ (5).
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For example, if you reach :strong:`MaxSessions` sessions you may get the
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following output:
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.. code-block:: sh
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$ cdist config -b -j 11 -v 78.47.116.244
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INFO: cdist: version 4.2.2-55-g640b7f9
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INFO: 78.47.116.244: Running global explorers
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INFO: 78.47.116.244: Remote transfer in 11 parallel jobs
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channel 22: open failed: administratively prohibited: open failed
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mux_client_request_session: session request failed: Session open refused by peer
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ControlSocket /tmp/tmpuah6fw_t/d886d4b7e4425a102a54bfaff4d2288b/ssh-control-path already exists, disabling multiplexing
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INFO: 78.47.116.244: Running global explorers in 11 parallel jobs
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channel 22: open failed: administratively prohibited: open failed
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mux_client_request_session: session request failed: Session open refused by peer
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ControlSocket /tmp/tmpuah6fw_t/d886d4b7e4425a102a54bfaff4d2288b/ssh-control-path already exists, disabling multiplexing
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INFO: 78.47.116.244: Running initial manifest /tmp/tmpuah6fw_t/d886d4b7e4425a102a54bfaff4d2288b/data/conf/manifest/init
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INFO: 78.47.116.244: Running manifest and explorers for __file/root/host.file
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INFO: 78.47.116.244: Generating code for __file/root/host.file
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INFO: 78.47.116.244: Finished successful run in 18.655028820037842 seconds
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INFO: cdist: Total processing time for 1 host(s): 19.159148693084717
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