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#summary PPSS Manual (Distributed)
#labels Featured
= Introduction =
To use PPSS in a distributed fasion, The following steps must be performed:
# Setup SSH access on server and nodes.
# Create a list of all nodes.
# Create a configuration file for PPSS, that will be distributed to nodes.
# Optional: create a custom script to be executed.
# Deploy PPSS to the nodes.
# Start PPSS on all nodes.
== Preparation of server and nodes ==
The following preparations must be made in order to use PPSS in a distributed fasion:
* Create an unprivileged user 'ppss' on the server.
* Create an unprivileged user 'ppss' on each node.
* Generate a SSH key without a pass phrase.
Example:
`ssh-keygen -f ppss-private.key`
{{{
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in ppss-private.key.
Your public key has been saved in ppss-private.key.pub.
The key fingerprint is:
....
bash-3.2$ ls -alh
total 16
drwxr-xr-x 4 ppss staff 136B 15 mrt 00:09 .
drwxr-xr-x+ 51 ppss staff 1,7K 14 mrt 17:45 ..
-rw------- 1 ppss staff 1,6K 15 mrt 00:09 ppss-private.key
-rw-r--r-- 1 ppss staff 401B 15 mrt 00:09 ppss-private.key.pub
}}}
The result is a private and a public key (.pub). The private key is the key that needs to be distributed to all nodes in order to be able to logon to the server.
* Add the public SSH key to the authorized_keys file of the 'ppss' user on the server.
Thus, put the contents of ppss-private.key.pub into a file called authorized_keys and place this file into the directory .ssh in the home directory of the PPSS user on the server.
* Add the public SSH key to the authorized_keys file of the 'ppss' user on the client.
This is necessary if you want to deploy PPSS on the nodes using PPSS in an automated fashion. The alternative is to manually copy PPSS and all necessary files to each node by hand.
* Create a 'known_hosts' file containing the public key of the server. *Important*
When a node connects to the server for the first time, SSH wil show you the fingerprint of the server and ask if it is ok to connect to this host. To prevent this question, you must perform one of these actions:
* Logon to each node manually and connect once to the server and manually accept the server signature
* Manually upload a known_hosts file to each node and place it in the .ssh directory.
* Create a file called "known_hosts" and put the server public key in this file. You may already have the server public key in the ~/.ssh/known_hosts file of a system that has been used to logon to the server.
Place the file in the same directory as where the ppss.sh script resides. When PPSS is deployed to the nodes, this 'known_hosts' file will be copied with the ppss.sh script to the nodes. This known_hosts file will be used by PPSS so in this case the first option, to manually logon to each node, is not necessary.
* Place PPSS on the server within the PPSS home directory.
*Security*
Please note that usage of SSH keys without pass phrases may pose a security threat if the machines are shared with other users. You must decide for yourself if the security risk that is associated with this setup is acceptable for your environment. For example, if a node is compromised, the attacker will have (initially unprivileged) access to the server.
== Create a list of nodes ==
A file must be created containing the hostnames (DNS) and/or IP-addresses of all nodes. The file must contain one node per line, such as:
{{{
192.168.0.100
192.168.0.101
host.domain.com
...
}}}
== Create a PPSS configuration file ==
This is the most important part of setting up distributed PPSS. It is exactly the same as setting up a configuration file for standalone mode, except that more options are necessary.
The best way to explain how to create a configuration file for distributed PPSS is to provide an example. In this example, a script is used to encode WAV files to MP3. This script is called 'encode.sh' and takes a filename as an argument.
`./ppss config -C config.cfg -c 'encode.sh ' -d /source/dir -s 192.168.1.100 -u ppss -k ppss-key.key -S ./encode.sh -n nodes.txt -t -o /some/output/dir`
It is quite a long command line, however, it is executed only once. Afther that, the config file config.cfg can be used for all further commands.
*Mode*
The first option sets the mode, in this case 'config' to generate a configuration file.
*Configuration file*
The second option, -C, specifies the name of the configuration file to be created.
*Command*
The third option, -c, specifies the command to be executed. *Please take special note of the single quotes and the space behind the command.* You can read -c 'encode.sh ' also as -c 'encode.sh "$ITEM"'.
*Source directory*
This option specifies the location on the *server* where the files reside that must be processed. These files will be transfered using SCP to the nodes for local processing.
*Server*
The -s option specifies the SSH server that acts as both fileserver and SSH server for communication between nodes. The SSH server is mainly used for file-locking: nodes know that locked files are already processed or being processed, so another unlocked file must be selected.
If the server acts both as a file server and SSH server, it is not recommended to use it also as a node, in this case for encoding. Filetransers using SSH can take quite some processing power.
*User name*
This is the name of the local system user that is used by the nodes to logon to the server with SSH. For deployment, such a user must also be present on the nodes.
*SSH Key*
Scripts using SSH require an SSH key withouth a passphrase. This key must be uploaded to the nodes an the nodes must know which key to use, so it must be specified.
*Script or program that must be uploaded*
The -S option specifies the script or program that should be uploaded to the node because it must be executed by the node for distributed computing. In this case, the encode.sh script must be deployed on all nodes and thus specified.
*List of nodes*
The -n option specifies the file containing all nodes. For every node, PPSS will perform actions such as deploy, start, stop and pause.
*Transfer files to local host*
If this option is specified, the file is copied from the source directory to a local temporary working directory for local processing. This is necessary if SCP is used to access files that must be processed.
If files are distributed over NFS or SMB, the files seem to be present on the local system, because it is just a mount point and thus just a part of the local file system. In this case, the -t option can be omitted, however it it is specified, files are copied to a local directory using 'cp'.
*The output directory*
If the -t option is used, the -o option specifies the destination directory on the server. The results are uploaded to this directory. If the -t option is not specified, the command 'cp' is used to transfer files back to the specified output directory.
*More examples*
The following example does the exact same thing as the encode script.
`./ppss config -C config.cfg -c 'lame -a "$ITEM" "$OUTPUT_DIR/$OUTPUT_FILE.mp3" --preset standard --quiet' -d /source/dir -s 192.168.1.100 -u ppss -k ppss-key.key -S ./encode.sh -n nodes.txt -t -o /some/output/dir`
The OUTPUT_DIR and OUTPUT_FILE variables are special. It tells your command where to store the output. This is important if you want to transfer the results of your command back to the server.
In this example, Lame requires that the user specifies an output file. PPSS generates the name of this output file for you, based on the name of the Item. This example shows that you don't need to create your own shell scripts in order to be able to use PPSS.
== Create a script ==
*Entirely optional!*
This section is optional. It is possible to execute commands just by using the -c option and the appropriate variables.
PPSS transfers files to the node and uploads the output back to the server. In order to be able to upload output back to the server, PPSS must know where this output can be found.
by default output is stored in the directory specified by $PPSS_LOCAL_OUTPUT/$ITEM. Ofcource, you can hard-code the PPSS_LOCAL_OUTPUT path, however, it is much easier to just source the ppss configuration file and use the already defined variables, that are used by PPSS anyway.
An example script that uses the settings of the PPSS configuration file is shown below, that has actually been used to encode 400 GB of WAV files.
{{{
#!/bin/bash
ITEM="$1"
TMP=`basename $ITEM`
source config.cfg
lame -a "$ITEM" "$PPSS_LOCAL_OUTPUT/$TMP/$TMP.mp3" --preset standard --quiet
ERROR="$?"
if [ "$ERROR" == "0" ]
then
echo "Encode of $ITEM successful."
exit 0
else
echo "Error when encoding $ITEM."
exit 1
fi
}}}
Take notice of the basename command. Items are provided with full path. Basename strips this path from the filename and uses just the filename in this script.
*Rules when writing a script for usage with PPSS*
* As with any decent shell script, use exit codes. Exit code 0 reflects successful execution, any other value a faillure.
* Echo some information about what the script is doing. If something fails, echo what is wrong. This is caught by PPSS and logged in the logfile of the item that is processed.
For example, the above script results in this kind of output:
{{{
===== PPSS Item Log File =====
Host: Beest
Item: PPSS_LOCAL_TMPDIR/20060907.wav
Start date: Mar 10 23:54:04
Encode of PPSS_LOCAL_TMPDIR/20060907.wav successful.
Status: Succes - item has been processed.
Elapsed time (h:m:s): 0:1:44
}}}
*TIP*
All variables specified when generating a configuration script can be used within your own script when sourcing the configuration file.
== Deploy PPSS to nodes ==
Once SSH access is setup and the configuration file is generated, PPSS can be deployed to the nodes. This is very simple, as this example demonstrates:
`./ppss.sh deploy -C config.cfg
During the phase when we generated the configuration file, a nodes file was specified. Thus PPSS knows, just by reading this configuration file, which file contains a list of nodes.
{{{
bash-3.2$ ./ppss.sh deploy -C config.cfg
mrt 12 22:18:22: INFO - ---------------------------------------------------------
mrt 12 22:18:22: INFO - Distributed Parallel Processing Shell Script version 2.03
mrt 12 22:18:22: INFO - Hostname: MacBoek.local
mrt 12 22:18:22: INFO - Deploying PPSS on nodes.
mrt 12 22:18:24: INFO - PPSS installed on node 192.168.1.14.
mrt 12 22:18:28: INFO - PPSS installed on node 192.168.1.12.
mrt 12 22:18:29: INFO - PPSS installed on node 192.168.1.4.
mrt 12 22:18:31: INFO - PPSS installed on node 192.168.1.31.
}}}
Deployment of PPSS is executed in parallel for each host.
== Start PPSS on nodes ==
Just as simple as deploying PPSS, PPSS is started on all nodes.
`./ppss.sh start -C config`
{{{
mrt 12 22:21:17: INFO - ---------------------------------------------------------
mrt 12 22:21:17: INFO - Distributed Parallel Processing Shell Script version 2.03
mrt 12 22:21:17: INFO - Hostname: MacBoek.local
mrt 12 22:21:17: INFO - Starting PPSS on node 10.0.0.14.
mrt 12 22:21:17: INFO - Starting PPSS on node 10.0.0.12.
mrt 12 22:21:20: INFO - Starting PPSS on node 10.0.0.4.
mrt 12 22:21:20: INFO - Starting PPSS on node 10.0.0.31.
}}}
== Stop pause and continue PPSS on nodes ==
To stop, pause or continue processing on all nodes, use the following commands:
`./ppss.sh stop -C config.cfg`
`./ppss.sh pause -C config.cfg`
`./ppss.sh continue -C config.cfg`
Please note that nodes will continue processing the current item they are working on, they just stop processing new items if stop or pause is selected.
== Show progress ==
The overall process of the 'cluster' is determined by the number of files present in the input and output directories on the server.
{{{
bash-3.2$ ./ppss.sh status -C config.cfg
mrt 12 21:06:17: INFO - ---------------------------------------------------------
mrt 12 21:06:17: INFO - Distributed Parallel Processing Shell Script version 2.03
mrt 12 21:06:17: INFO - Hostname: MacBoek.local
mrt 12 21:06:17: INFO - 56 percent complete.
}}}
== Logging ==
An important feature of PPSS is its extensive logging. There are two types of log files.
* A single log file created by PPSS itself. This file is found on the local nodes. Using tail -f on these files, it is possible to monitor what PPSS is currently doing.
{{{
Mar 12 22:57:19: INFO - ---------------------------------------------------------
Mar 12 22:57:19: INFO - Distributed Parallel Processing Shell Script version 2.03
Mar 12 22:57:19: INDO - ---------------------------------------------------------
Mar 12 22:57:19: INFO - Hostname: Beest
Mar 12 22:57:19: DEBUG - Found 8 logic processors.
Mar 12 22:57:19: INFO - CPU: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz
Mar 12 22:57:19: INFO - ---------------------------------------------------------
Mar 12 22:57:19: DEBUG - Job log directory JOB_LOG exists.
Mar 12 22:57:20: INFO - Listener started.
Mar 12 22:57:20: INFO - Starting 8 workers.
Mar 12 22:57:20: INFO - Currently 0 percent complete. Processed 0 of 625 items.
Mar 12 22:57:20: DEBUG - Trying to lock item 20060731.wav.
Mar 12 22:57:20: DEBUG - Item 20060731.wav is locked.
Mar 12 22:57:20: INFO - Currently 0 percent complete. Processed 1 of 625 items.
Mar 12 22:57:20: DEBUG - Trying to lock item 20060801.wav.
Mar 12 22:57:20: DEBUG - Item 20060801.wav is locked.
Mar 12 22:57:20: INFO - Currently 0 percent complete. Processed 2 of 625 items.
Mar 12 22:57:20: DEBUG - Trying to lock item 20060802.wav.
Mar 12 22:57:20: DEBUG - Item 20060802.wav is locked.
Mar 12 22:57:20: INFO - Currently 0 percent complete. Processed 3 of 625 items.
............
mrt 10 23:51:23: DEBUG - Item 20060830.wav is locked.
mrt 10 23:51:23: INFO - Currently 3 percent complete. Processed 23 of 625 items.
mrt 10 23:51:23: DEBUG - Trying to lock item 20060831.wav.
mrt 10 23:51:23: DEBUG - Got lock on 20060831.wav, processing.
mrt 10 23:51:23: DEBUG - Transfering item 20060831.wav to local disk.
mrt 10 23:52:18: DEBUG - Exit code of transfer is 0
mrt 10 23:52:18: DEBUG - Processing item 20060831.wav
}}}
* An individual log file containing information and output of each processed item. these files are uploaded to the SSH server to the 'job_log' directory. For every item, a log file must be present.
{{{
===== PPSS Item Log File =====
Host: MacBoek.local
Item: PPSS_LOCAL_TMPDIR/20060831.wav
Start date: mrt 10 23:52:18
Encode of PPSS_LOCAL_TMPDIR/20060831.wav successful.
Status: Succes - item has been processed.
Elapsed time (h:m:s): 0:5:23
}}}
As you can see, with a few simple grep commands, it is possible to quickly determine which items have failed to process. Also, you can see that my MacBook took 5 minutes and 23 seconds to process this WAV file.
Please note that the "Encode of..." part is output of the script that is executed on an item. The other content is generated by PPSS.
== To wrap it up ==
I am convinced that PPSS is very easy to use and tailored to your needs. If you have questions and/or suggestions, don't hesitate to send an e-mail. If you find bugs, please report them using the issue tracker. Feedback is greatly appreciated.
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