Running the NCI-GDC DNA-Seq workflow

In this section, we will guide you through the steps to run the NCI-GDC’s DNA-Seq harmonization workflow on Google Compute Engine. This workflow is available on github here. The instructions here are based on the NCI-GDC’s README and have been customized to run on GCE.

1. Create a GCE VM with Disk

From the Cloud Console > Compute Engine > VM instances page click on [+] CREATE INSTANCE, and:

  • set Name (eg cwl-test-1)

  • set Zone (eg us-central1-c)

  • set Machine type (eg 4 vCPUs with 15 GB memory)

  • Change the boot disk to Ubuntu 14.04 LTS with 10 GB standard persistent disk (note that the boot disk will be named the same as the VM, ie cwl-test-1)

  • leave the Identity and API access box as is (with “Compute Engine default service account” and “Allow default access” selected)

  • expand the “Management, disk, networking, SSH keys section”:

    • select the Disks tab

    • click on + Add item

    • in the Name pull-down, select “Create disk”: a “Create a disk” panel will open:

      • set Name (eg cwl-disk-1) – do not use the same name as the VM!
      • set Source type to “None (blank disk)”
      • set Size (eg 500 GB)
      • leave default Encryption (which is “Automatic (recommended)”)
      • click on the blue Create button – this will create the disk only at this time
    • before clicking on the Create button (for the VM), click on the bottom line where it says “Equivalent REST or command line” – you can save this command-line and re-use it later to create the same VM from the command-line rather than repeating this interactive process; it is also a nice record of exactly how the VM was created

    • now click on the Create button – you will see the VM “spinning up” on the VM instances page

Example command-line equivalents to create the disk and the VM (you will need to substitute in your own Google Cloud Platform (GCP) project:

$ gcloud compute --project <YOUR-PROJECT-ID> disks create "cwl-disk-1" --size "500" --zone "us-central1-c" --type "pd-standard"

$ gcloud compute --project <YOUR-PROJECT-ID> instances create "cwl-test-1" --zone "us-central1-c" --machine-type "n1-standard-4" --network "default" --maintenance-policy "MIGRATE" --scopes default="","","","","","" --disk "name=cwl-disk-1,device-name=cwl-disk-1,mode=rw,boot=no" --image "/ubuntu-os-cloud/ubuntu-1404-trusty-v20161205" --boot-disk-size "10" --boot-disk-type "pd-standard" --boot-disk-device-name "cwl-test-1"

2. Configure the VM

Now you can ssh to your VM from any command-line where you have the cloud SDK installed. If you don’t have the cloud SDK installed on your local machine, you can use the Cloud Shell directly from your browser in the Cloud Console.

$ gcloud compute --project <YOUR-PROJECT-ID> ssh --zone "us-central1-c" "cwl-test-1"

2.1 Install Packages

Use the following commands to install the necessary packages:

$ sudo apt-key adv --keyserver hkp:// --recv-keys 58118E89F3A912897C070ADBF76221572C52609D

$ echo "deb ubuntu-trusty main" | sudo tee /etc/apt/sources.list.d/docker.list

$ sudo aptitude update

$ sudo aptitude install apt-transport-https ca-certificates docker-engine htop libffi-dev libssl-dev nodejs python-dev virtualenvwrapper

After this last command, you will need to respond “Yes” to install the new packages.

2.2 Format and Mount the Disk

You can see the disks that are attached to your VM by using the following command:

$ ls /dev/disk/by-id

which should respond with something like:

google-cwl-disk-1  google-cwl-test-1-part1                 scsi-0Google_PersistentDisk_cwl-test-1
google-cwl-test-1  scsi-0Google_PersistentDisk_cwl-disk-1  scsi-0Google_PersistentDisk_cwl-test-1-part1

The first disk listed above (google-cwl-disk-1) is the additional disk that was crated, while the second one (google-cwl-test-1) is the boot disk, with the same name as the VM. The following commands differ slightly from those specified in the NCI-GDC README but the result will be the same:

$ sudo mkfs.ext4 -F -E lazy_itable_init=0,lazy_journal_init=0,discard /dev/disk/by-id/google-cwl-disk-1
$ sudo mkdir -p /mnt/SCRATCH
$ sudo mount -o discard,defaults /dev/disk/by-id/google-cwl-disk-1 /mnt/SCRATCH
$ sudo chmod 777 /mnt/SCRATCH

You can now verify that the disk has been properly mounted using the df -h command:

$ df -h

File system      Size    Used    Avail    Use%    Mounted on
/dev/sdb         493G     70M     467G      1%    /mnt/SCRATCH

and as you can see, close to 500G of space is available mounted as /mnt/SCRATCH.

2.3 Prepare Docker and CWL

These next sets of commands will get you ready to run docker on this VM. You will need to log out and log back in a couple of times to force certain changes to take effect.

$ mkdir /mnt/SCRATCH/docker
$ sudo bash -c 'echo DOCKER_OPTS=\"-g /mnt/SCRATCH/docker/\" >> /etc/default/docker'
$ sudo gpasswd -a ${USER} docker
$ sudo service docker restart
$ exit

The last command will log you out of your VM, so you will need to log back in using the same gcloud ssh command you used before. Once you’re back on the VM:

$ echo "source /usr/share/virtualenvwrapper/" >> ~/.bashrc
$ exit

Sign back in again, and then create a “virtualenv” called “cwl”. This will change your command-line prompt to indicate that you are in a new environment:

$ mkvirtualenv --python /usr/bin/python2 cwl
(cwl) $

A few more install commands and you’ll be ready to go:

(cwl)$ pip install --upgrade pip
(cwl)$ pip install 'requests[security]' --no-cache-dir
(cwl)$ wget
(cwl)$ pip install 1.0_gdc_g.tar.gz --no-cache-dir

3. Run the DNA-Seq workflow

3.1 Clone the NCI-GDC github repo

You should now be in your home directory, in the (cwl) virtualenv. Clone the NCI-GDC dna-seq-cwl repo:

(cwl)$ git clone

Now you will have a subdirectory called gdc-dnaseq-cwl in your home directory, containing the NCI-GDC DNA-Seq harmonization workflow. The main workflow is in the CWL file ~/gdc-dnaseq-cwl/workflows/dnaseq/transform.cwl.

3.2 Load Reference and Input Data Files

The DNA-Seq workflow requires some reference data files that can be obtained from the NCI-GDC. These include the dbsnp vcf (3 GB), the reference genome (835 MB), and the bwa indexed genome (3.2 GB). (Uploading these to your VM disk should take 5-10 minutes.)

(cwl)$ mkdir /mnt/SCRATCH/hg38_reference
(cwl)$ cd /mnt/SCRATCH/hg38_reference
(cwl)$ wget -O dbsnp_144.hg38.vcf.gz
(cwl)$ wget
(cwl)$ tar xvf 62f23fad-0f24-43fb-8844-990d531947cf
(cwl)$ wget
(cwl)$ tar xvf 964cbdac-1043-4fae-b068-c3a65d992f6b

Finally, let’s copy a small example BAM file (300 MB) from the 1000G repository:

(cwl)$ cd /mnt/SCRATCH
(cwl)$ wget

At this point you could also obtain a bam file either from the NCI-GDC or from one of the ISB-CGC Cloud Storage buckets.

3.3 Run DNA-Seq CWL workflow

Now we’re ready to run the workflow using the CWL-runner cwltool. The input file that we just copied to our VM disk is in /mnt/SCRATCH/alignment/NA12878.chrom20.ILLUMINA.bwa.CEU.low_coverage.20121211.bam. Let’s create a sub-directory for the processed results:

(cwl)$ mkdir /mnt/SCRATCH/NA12878.chrom20.ILLUMINA.bwa.CEU.low_coverage.20121211
(cwl)$ cd /mnt/SCRATCH/NA12878.chrom20.ILLUMINA.bwa.CEU.low_coverage.20121211
(cwl)$ mkdir tmp cache
(cwl)$ nohup cwltool --debug --tmpdir-prefix tmp/ --cachedir cache/ \
         ~/gdc-dnaseq-cwl/workflows/dnaseq/transform.cwl \
         ~/gdc-dnaseq-cwl/workflows/dnaseq/NA12878.chrom20.ILLUMINA.bwa.CEU.low_coverage.20121211.json &

While that is running, you can go back to the Cloud Console, to the Compute Engine > VM instances page, and click on the name of this VM. This will take you to a page describing this specific VM, and you can see a trace of CPU utilization, and other metrics.

Let’s also take a closer look at the cwltool command used above. You can find more details at the cwltool github repo and at The basic form of the cwltool command is:

$ cwltool [tool-or-workflow-description] [input-job-settings]

Looking at the way cwltool was invoked above, we see that the tool-or-workflow-description is in ~/gdc-dnaseq-cwl/workflows/dnaseq/transform.cwl and the input-job-settings are in ~/gdc-dnaseq-cwl/workflows/dnaseq/NA12878.chrom20.ILLUMINA.bwa.CEU.low_coverage.20121211.json. Let’s have a closer look at those, starting with the smaller input-job-settings JSON document. It defines three objects, each of which is of class “File”, with a specified “path”, eg:

"bam_path": {
    "class": "File",
    "path": "/mnt/SCRATCH/NA12878.chrom20.ILLUMINA.bwa.CEU.low_coverage.20121211.bam"

and it also specifies a “thread_count” value (8), and a “uuid”. You can see these inputs defined near the top of the CWL document (transform.cwl).

3.4 Run-time and Compute-costs

This sample task takes about 2 hours to run. The costs associated with running this task are: 2 hours of GCE VM time plus 2 hours of persistent disk time (GCE pricing details), which comes to approximately $0.400 for the VM and $0.056 for the persistent disks, for a total of $0.456. (The n1-standard-4 VM chosen above costs $0.200 per hour, and the disk costs, at $0.040 per GB per month for standard provisioned space, were computed as 510 GB x $0.040 per GB per month x 2 hours / 730 hours per month.)

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