HTCondor in the Cloud

Although any HTCondor pool for which each node was running on a cloud resource could fairly be described as a “HTCondor in the Cloud”, in this section we concern ourselves with creating such pools using condor_annex. The basic idea is start only a single instance manually – the “seed” node – which constitutes all of the HTCondor infrastructure required to run both condor_annex and jobs.

The HTCondor in the Cloud Seed

A seed node hosts the HTCondor pool infrastructure (the parts that aren’t execute nodes). While HTCondor will try to reconnect to running jobs if the instance hosting the schedd shuts down, you would need to take additional precautions – making sure the seed node is automatically restarted, that it comes back quickly (faster than the job reconnect timeout), and that it comes back with the same IP address(es), among others – to minimize the amount of work-in-progress lost. We therefore recommend against using an interruptible instance for the seed node.


Your cloud provider may allow you grant an instance privileges (e.g., the privilege of starting new instances). This can be more convenient (because you don’t have to manually copy credentials into the instance), but may be risky if you allow others to log into the instance (possibly allowing them to take advantage of the instance’s privileges). Conversely, copying credentials into the instance makes it easy to forget to remove them before creating an image of that instance (if you do).

Making a HTCondor in the Cloud

The general instructions are simple:

  1. Start an instance from a seed image. Grant it privileges if you want. (See above).
  2. If you did not grant the instance privileges, copy your credentials to the instance.
  3. Run condor_annex.

AWS-Specific Instructions

The following instructions create a HTCondor-in-the-Cloud using the default seed image.

  1. Go to the EC2 console.
  2. Click the ‘Launch Instance’ button.
  3. Click on ‘Community AMIs’.
  4. Search for Condor-in-the-Cloud Seed. (The AMI ID is ami-00eeb25291cfad66f.) Click the ‘Select’ button.
  5. Choose an instance type. (Select m5.large if you have no preference.)
  6. Click the ‘Next: Configure Instance Details’ button.
  7. For ‘IAM Role’, select the role you created in Using Instance Credentials, or follow those instructions now.
  8. Click ‘6. Configure Security Group’. This creates a firewall rule to allow you to log into your instance.
  9. Click the ‘Review and Launch’ button.
  10. Click the ‘Launch’ button.
  11. Select an existing key pair if you have one; you will need the corresponding private key file to log in to your instance. If you don’t have one, select ‘Create a new key pair’ and enter a name; ‘HTCondor Annex’ is fine. Click ‘Download key pair’. Save the file some place you can access easily but others can’t; you’ll need it later.
  12. Click through, then click the button labelled ‘View Instances’.
  13. The IPv4 address of your seed instance will be display. Use SSH to connect to that address as the ‘ec2-user’ with the key pair from two steps ago.

To grow your new HTCondor-in-the-Cloud from this seed, follow the instructions for using condor_annex for the first time, starting with Configure condor_annex. You can than proceed to Start an Annex.

Creating a Seed

A seed image is simply an image with:

  • HTCondor installed
  • HTCondor configured to:
    • be a central manager
    • be a submit node
    • allow condor_annex can add nodes
  • a small script to set TCP_FORWARDING_HOST to the instance’s public IP adress when the instance starts up.

More-detailed instructions for constructing a seed node on AWS are available. A RHEL 7.6 image built according to those instructions is available as public AMI ami-00eeb25291cfad66f.