Computing Element Guide¶

This guide provides instructions on setting up JAliEn Computing Element (CE) by either running directly from CVMFS (Option 1), or by cloning the JAliEn Git repository (Option 2).

Option 1: Running from CVMFS¶

This approach only requires CVMFS and a valid Grid certificate or a user/host token in ~/.globus. It is the simplest approach for getting a CE up and running, but configuration is limited to the options given in the config files.

Ensure environment path for the proxy certificate is set. See output from voms-proxy-info -path to get the full path, for example:
```
~$ export X509_USER_PROXY='/var/lib/vobox/alice/proxy_repository/+2fDC+3dch+2fDC...'
```

Load the JAliEn environment:

#If not in path, can be found at `/cvmfs/alice.cern.ch/bin/alienv`.
~$ alienv enter JAliEn

Run the CE:
```
~$ jalien alien.site.ComputingElement
```

This will start a JAliEn CE with default configuration options. Override is possible by placing desired configuration in ~/.j/config. Overview of the config files, and their default values, can be found here.

User/Host token

User and host tokens can be generated from within a JAliEn shell by using token -t user/host command. These can be put as user[cert/key].pem into .globus folder, instead of a full Grid certificate.

Option 2: Compile From Source¶

Requirements

This approach requires compile tools such as JDK11+ be available.

This approach gives access to the latest CE changes without waiting for a new tag to be pushed to CVMFS. JobAgents will still run from CVMFS, but their startup script may now be modified - allowing for changes such as what variables are exported, scripts are run before start, and containers may also be enabled/disabled as desired. Other in-code overrides are also possible (at own risk). As with the first option, a valid Grid certificate or a user/host token in ~/.globus is required.

Clone the JAliEn Git repository:

~$ git clone https://gitlab.cern.ch/jalien/jalien.git

Compile JAliEn using the following commands, adjusting configuration in jalien/config as needed beforehand.
```
~$ cd jalien
~$ ./compile.sh all
```
Ensure environment path for the proxy certificate is set. See output from voms-proxy-info -path to get the full path, for example:
```
~$ export X509_USER_PROXY='/var/lib/vobox/alice/proxy_repository/+2fDC+3dch+2fDC...'
```
Run the CE as follows:
```
~$ ./jalien ComputingElement
```

Managing the CE¶

A wrapper script can be used to shortcut common tasks such as start, stop and checking the service status:

Example: jalienCE.sh

#!/bin/bash

export X509_USER_PROXY=
export ALICE_LOGDIR= #e.g ~/ALICE/alien-logs
export JALIEN_PATH= #e.g ~/jalien (remove if running from CVMfS)

cd $ALICE_LOGDIR

if [ $1 = "start" ]
  then
    echo "Starting JAliEn CE"
    nohup $JALIEN_PATH/jalien ComputingElement & echo $! > CE.pid
elif [[ $1 = "stop" ]]
  then
    echo "Stopping JAliEn CE"
    pkill -f alien.site.ComputingElement
elif [ $1 = "status" ]
  then
   if ps -p $(cat $ALICE_LOGDIR/CE.pid) > /dev/null 2>&1
   then
      echo "JAliEn CE is running"
   else
      echo "JAliEn CE is NOT running!"
   fi 
else 
    echo "Usage: 'start', 'stop' or 'status'" 
fi

Be aware that the JAliEn CE will terminate once the token expires. To avoid downtime, a service can be set up to automatically restart it once that happens. A trivial solution can be to extend the above wrapper script with a restarter as follows:

Example: jalien-restarter.sh

#!/bin/bash

JALIEN_CE_WRAPPER=~/jalienCE.sh

while true
do
   if [ "$($JALIEN_CE_WRAPPER status)" = "JAliEn CE is running" ]
   then
      echo "OK"
   else
      echo "Not OK"
      $($JALIEN_CE_WRAPPER start)
   fi
sleep  1800
done

FAQ¶

What about logs?

The JAliEn CE log directory is defined in LDAP, the same way as for legacy AliEn. A common directory used is ~/ALICE/alien-logs.

What about updates?

When using option 1 (CE in CVMFS), the CE can be updated by simply reloading the CE and alienv, activating the latest tag. For option 2 (CE from git), the latest version can be obtained by doing a git pull and compile.sh all, before restarting.

No action is needed for the JobAgents, as these are always started using the same (or closest available) tag as the CE through CVMFS.