Quickstart ARC: towards distributed computing in a few minutes - token edition

Scared of distributed computing complexities?

With ARC7 you can setup a Computing Element and try common distributed computing workflows in just a few minutes!

ARC7 comes with so-called zero configuration included and works out of the box without any manual configuration. It has a pre-installed x509 host certificate signed by a Test-CA.

If you want to test your ARC-CE with token submission there are two extra steps that need to be performed in order to set up a Test JWT issuer and allow the client (remote client or on the ARC-CE itself) to trust tokens from this issuer.

If you want to test job submission on a remote ARC client, the client must trust the ARC-CE host certificate which is issued by the Test-CA, and you must therefore apply the extra step for both the token and the x509 user case. These are described in Step 5c or Step 5b respectively.

You can try ARC by using the legacy x509 user certificate, or with the newer Jason Web Token capability. The procedure below splits into x509 versus token at Step 5. The two require slightly different configuration options on the ARC server, and different procedures to aquire the authentication document (certificate or token).

The ARC server can be set up to accept both user x509 certificates and user tokens in paralell, or just one of the two. This is up to you.

Step 0. Prerequisites

  • The zero configured A-REX comes with the REST interface enabled. It runs by default on port 443, so make sure it is not firewalled.

  • If you are testing ARC with a remote client: Either register your ARC-CE on a DNS server, or add the ARC-CE host name to the /etc/hosts file on the client host.

Step 1. Enable NorduGrid ARC7 repos

Repository security

The NorduGrid RPM packages and DEB repositories are signed, and in order for the repository tools APT and YUM to verify them you must install the NorduGrid GPG key:

For rpm based distributions like Red Hat Enterprise Linux and Fedora:

[root ~]# rpm --import http://download.nordugrid.org/RPM-GPG-KEY-nordugrid-7

Repository configuration

The NorduGrid ARC repositories for RedHat Enterprise Linux / CentOS packaging utility dnf can be configured through: /etc/yum.repos.d/nordugrid.repo

The repository configuration can be set up automatically with dnf by installing the``nordugrid-release`` package or creating the configuration file manually.

The easiest way to configure DNF to use the NorduGrid repository for Red Hat Enterprise Linux, CentOS and similar distributions is to install the nordugrid-release package which can be found in the NorduGrid package repository for the appropriate RHEL/EPEL release.

Links to the release packages:

Rocky Linux: 9 8

Install with dnf (Fedora, CentOS Stream, Rocky Linux, CentOS Linux 8+9) by copying the appropriate link from above

[root ~]# dnf install <rhel-repo link>

This creates the appropriate repo files in /etc/yum.repos.d/.

Set up dependency repositories

dnf config-manager --set-enabled powertools
dnf makecache

Step 2. Install A-REX

ARC Resource-coupled EXecution service (A-REX) is a core component that manages authentication, authorization and job life cycle. It is enough to have A-REX installed to have a minimal computing element:

[root ~]# dnf -y install nordugrid-arc-arex

Step 3. Run A-REX

To start ARC services just run:

[root ~]# arcctl service start --as-configured

You can check if A-REX is running with:

[root ~]# arcctl service list
arc-arex                         (Installed, Disabled, Running)
arc-arex-ws                      (Installed, Disabled, Running)
arc-datadelivery-service         (Not installed, Disabled, Stopped)
arc-infosys-ldap                 (Not installed, Disabled, Stopped)

Step 4. Install the ARC client

Install ARC client tools on the client host

Note

In the zero-conf setup - we install the client and the ARC control client tool on the same server as the ARC-CE, so client and host is the same machine. Typically you would install the client on amother (remote) machine.

[root@server]# dnf -y install nordugrid-arc-client nordugrid-arc-arcctl

Step 5. Install and enable autocompletion (optional)

arcctl tool automates many ARC CE operations and is designed with bash-completion in mind. If you would like to use ARC in production it is advised to have completion enabled:

[root ~]# dnf install -y bash-completion python-argcomplete
[root ~]# activate-global-python-argcomplete

Step 6. Set up test jwt token issuer and trust

If your ARC-CE and ARC client are the same machine you can apply the compressed command below that both initializes the test-jwt issuer and sets up the trust in one step.

[root@server]# $(arcctl test-jwt init --force | tail -n 1)

Step 7. Get a submission token

To submit jobs or perform any other action towards the ARC-CE you must authenticate yourself. We will do this using a token issued from the test-jwt issuer.

To generate a token do:

[user ~]$ export BEARER_TOKEN=$(arcctl test-jwt token)

Step 8. Restart A-REX

On the ARC-CE, restart A-REX services to activate the configuration changes

[root ~]# arcctl service restart -a

Step 9. Check all is ok

You can run the client commands (arcinfo, arcsub etc) from the host running A-REX or from any other machine by installing the ARC client in steps 4 and 5.

You can start with the information query about your newly installed ARC computing element:

[user ~]$ arcinfo -C https://arc.example.org/arex
Computing service:
  Information endpoint: https://arc.example.org:443/arex
  Submission endpoint: https://arc.example.org:443/arex (status: ok, interface: org.nordugrid.arcrest)

This means that all is ok, and the ARC client got back information from the ARC-CE that the information and service endpoints are available and ok.

Note

The examples use arc.example.org as a domain name for A-REX host. Step 0. Prerequisites for more information.

Tip: You can use $(hostname) instead of typing the hostname for these tests in your zero-conf setup and have a local client. For example:

arcinfo -C $(hostname)

Warning

It can take some minutes after the setup for everything to be fine, so if you see status: critical wait ca 1 minute and check again.

Step 10. Submit a job and check that it is running

A simple job can be submitted with the arctest tool:

[user ~]$ arctest -J 2 -C https://arc.example.org/arex
Job submitted with jobid: https://arc.example.org:443/arex/rest/1.0/jobs/f77b3d1b1efb

The job status can be checked with the arcstat tool:

[user ~]$ arcstat https://arc.example.org:443/arex/rest/1.0/jobs/f77b3d1b1efb
Job: https://arc.example.org:443/arex/rest/1.0/jobs/f77b3d1b1efb
 Name: arctest2
 State: Running

Status of 1 jobs was queried, 1 jobs returned information

To fetch the job’s stdout run arccat tool:

[user ~]$ arccat https://arc.example.org:443/arex/rest/1.0/jobs/f77b3d1b1efb
HOSTNAME=arc.example.org
GRID_GLOBAL_JOBURL=https://arc.example.org:443/arex/f77b3d1b1efb
MALLOC_ARENA_MAX=2
PWD=/var/spool/arc/sessiondir/f77b3d1b1efb
SYSTEMD_EXEC_PID=374194
<output_omitted>

Step 11. Play more with the ARC Computing Element

As an admin you might frequently need to extract information from the logs and directories that ARC computing element uses. The brief list of the relevant paths can be obtained from:

[root ~]# arcctl config brief
ARC Storage Areas:
    Control directory:
        /var/spool/arc/jobstatus
    Session directories:
        /var/spool/arc/sessiondir
    Scratch directory on Worker Node:
        Not configured
    Additional user-defined RTE directories:
        Not configured
ARC Log Files:
    A-REX Service log:
        /var/log/arc/arex.log
    A-REX Jobs log:
        /var/log/arc/arex-jobs.log
    A-REX Helpers log:
        /var/log/arc/job.helper.errors
    A-REX WS Interface log:
        /var/log/arc/ws-interface.log
    Infosys Infoproviders log:
        /var/log/arc/infoprovider.log

To get information and manage jobs on A-REX server, the arcctl job is useful. Operations include but is not limited to:

  • Listing jobs:

[root ~]# arcctl job list
f5ab040cdc51
f617259d58ec
<output omitted>

[root ~]# arcctl job list --long
f5ab040cdc51      FINISHED   arctest2                                https://wlcg.cloud.cnaf.infn.it//b9f1e5e2-a8f0-4332-bd9d-58bd63898cc6
f617259d58ec      FINISHED   arctest2                                https://wlcg.cloud.cnaf.infn.it//b9f1e5e2-a8f0-4332-bd9d-58bd63898cc6
<output omitted>

  • Job general information:

[root ~]# arcctl job info f77b3d1b1efb
Name         : arctest2
Owner        : https://wlcg.cloud.cnaf.infn.it//b9f1e5e2-a8f0-4332-bd9d-58bd63898cc6
State        : FINISHED
LRMS ID      : 376176
Modified     : 2023-06-02 16:07:05

  • Job log:

[root ~]# arcctl job log f77b3d1b1efb
2023-06-02T14:06:51Z Job state change UNDEFINED -> ACCEPTED   Reason: (Re)Accepting new job
2023-06-02T14:06:51Z Job state change ACCEPTED -> PREPARING   Reason: Starting job processing
2023-06-02T14:06:51Z Job state change PREPARING -> SUBMIT   Reason: Pre-staging finished, passing job to LRMS
----- exiting submit_fork_job -----

2023-06-02T14:06:53Z Job state change SUBMIT -> INLRMS   Reason: Job is passed to LRMS
---------- Output of the job wrapper script -----------
Detecting resource accounting method available for the job.
Looking for /usr/bin/time tool for accounting measurements
GNU time found and will be used for job accounting.
------------------------- End of output -------------------------
2023-06-02T14:07:05Z Job state change INLRMS -> FINISHING   Reason: Job finished executing in LRMS
2023-06-02T14:07:05Z Job state change FINISHING -> FINISHED   Reason: Stage-out finished.

  • A-REX logs that mentions the job:

[root ~]# arcctl job log f77b3d1b1efb --service
### /var/log/arc/arex.log:
[2023-06-02 16:06:51] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: ACCEPTED: parsing job description
[2023-06-02 16:06:51] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: ACCEPTED: moving to PREPARING
[2023-06-02 16:06:51] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: PREPARING from ACCEPTED
[2023-06-02 16:06:51] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: SUBMIT from PREPARING
[2023-06-02 16:06:51] [Arc] [INFO] [374270/3] f77b3d1b1efb: state SUBMIT: starting child: /usr/share/arc/submit-fork-job
[2023-06-02 16:06:53] [Arc] [INFO] [374270/3] f77b3d1b1efb: state SUBMIT: child exited with code 0
[2023-06-02 16:06:53] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: INLRMS from SUBMIT
[2023-06-02 16:07:05] [Arc] [INFO] [374270/3] f77b3d1b1efb: Job finished
[2023-06-02 16:07:05] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: FINISHING from INLRMS
[2023-06-02 16:07:05] [Arc] [INFO] [374270/3] f77b3d1b1efb: State: FINISHED from FINISHING
### /var/log/arc/ws-interface.log:

  • Getting job attributes:

[root ~]# arcctl job attr f77b3d1b1efb jobname
arctest2

Get production ready

Now you are ready to Install production ARC7 Computing Element!