---
layout: default
navsection: userguide
title: "Writing a CWL workflow"
...
{% comment %}
Copyright (C) The Arvados Authors. All rights reserved.
SPDX-License-Identifier: CC-BY-SA-3.0
{% endcomment %}
{% include 'what_is_cwl' %}
{% include 'tutorial_expectations' %}
h2. Developing workflows
For an introduction and and detailed documentation about writing CWL, see the "CWL User Guide":https://www.commonwl.org/user_guide and the "CWL Specification":http://commonwl.org/v1.0 .
See "Best Practices for writing CWL":{{site.baseurl}}/user/cwl/cwl-style.html and "Arvados CWL Extensions":{{site.baseurl}}/user/cwl/cwl-extensions.html for additional information about using CWL on Arvados.
h2. Using Composer
You can create new workflows in the browser using "Arvados Composer":{{site.baseurl}}/user/composer/composer.html
h2. Registering a workflow to use in Workbench
Use @--create-workflow@ to register a CWL workflow with Arvados. This enables you to share workflows with other Arvados users, and run them by clicking the <span class="btn btn-sm btn-primary"><i class="fa fa-fw fa-gear"></i> Run a process...</span> button on the Workbench Dashboard and on the command line by UUID.
<notextile>
<pre><code>~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">arvados-cwl-runner --create-workflow bwa-mem.cwl</span>
arvados-cwl-runner 1.0.20160628195002, arvados-python-client 0.1.20160616015107, cwltool 1.0.20160629140624
2016-07-01 12:21:01 arvados.arv-run[15796] INFO: Upload local files: "bwa-mem.cwl"
2016-07-01 12:21:01 arvados.arv-run[15796] INFO: Uploaded to qr1hi-4zz18-7e0hedrmkuyoei3
2016-07-01 12:21:01 arvados.cwl-runner[15796] INFO: Created template qr1hi-p5p6p-rjleou1dwr167v5
qr1hi-p5p6p-rjleou1dwr167v5
</code></pre>
</notextile>
You can provide a partial input file to set default values for the workflow input parameters. You can also use the @--name@ option to set the name of the workflow:
<notextile>
<pre><code>~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">arvados-cwl-runner --name "My workflow with defaults" --create-workflow bwa-mem.cwl bwa-mem-template.yml</span>
arvados-cwl-runner 1.0.20160628195002, arvados-python-client 0.1.20160616015107, cwltool 1.0.20160629140624
2016-07-01 14:09:50 arvados.arv-run[3730] INFO: Upload local files: "bwa-mem.cwl"
2016-07-01 14:09:50 arvados.arv-run[3730] INFO: Uploaded to qr1hi-4zz18-0f91qkovk4ml18o
2016-07-01 14:09:50 arvados.cwl-runner[3730] INFO: Created template qr1hi-p5p6p-0deqe6nuuyqns2i
qr1hi-p5p6p-zuniv58hn8d0qd8
</code></pre>
</notextile>
h3. Running registered workflows at the command line
You can run a registered workflow at the command line by its UUID:
<notextile>
<pre><code>~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">arvados-cwl-runner qr1hi-p5p6p-zuniv58hn8d0qd8 --help</span>
/home/peter/work/scripts/venv/bin/arvados-cwl-runner 0d62edcb9d25bf4dcdb20d8872ea7b438e12fc59 1.0.20161209192028, arvados-python-client 0.1.20161212125425, cwltool 1.0.20161207161158
Resolved 'qr1hi-p5p6p-zuniv58hn8d0qd8' to 'keep:655c6cd07550151b210961ed1d3852cf+57/bwa-mem.cwl'
usage: qr1hi-p5p6p-zuniv58hn8d0qd8 [-h] [--PL PL] --group_id GROUP_ID
--read_p1 READ_P1 [--read_p2 READ_P2]
[--reference REFERENCE] --sample_id
SAMPLE_ID
[job_order]
positional arguments:
job_order Job input json file
optional arguments:
-h, --help show this help message and exit
--PL PL
--group_id GROUP_ID
--read_p1 READ_P1 The reads, in fastq format.
--read_p2 READ_P2 For mate paired reads, the second file (optional).
--reference REFERENCE
The index files produced by `bwa index`
--sample_id SAMPLE_ID
</code></pre>
</notextile>
h2. Using cwltool
When developing a workflow, it is often helpful to run it on the local host to avoid the overhead of submitting to the cluster. To execute a workflow only on the local host (without submitting jobs to an Arvados cluster) you can use the @cwltool@ command. Note that when using @cwltool@ you must have the input data accessible on the local file system using either @arv-mount@ or @arv-get@ to fetch the data from Keep.
<notextile>
<pre><code>~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">arv-get 2463fa9efeb75e099685528b3b9071e0+438/ .</span>
156 MiB / 156 MiB 100.0%
~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">arv-get ae480c5099b81e17267b7445e35b4bc7+180/ .</span>
23 MiB / 23 MiB 100.0%
~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">cwltool bwa-mem-input.yml bwa-mem-input-local.yml</span>
cwltool 1.0.20160629140624
[job bwa-mem.cwl] /home/example/arvados/doc/user/cwl/bwa-mem$ docker \
run \
-i \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/19.fasta.ann:/var/lib/cwl/job979368791_bwa-mem/19.fasta.ann:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/HWI-ST1027_129_D0THKACXX.1_1.fastq:/var/lib/cwl/job979368791_bwa-mem/HWI-ST1027_129_D0THKACXX.1_1.fastq:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/19.fasta.sa:/var/lib/cwl/job979368791_bwa-mem/19.fasta.sa:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/19.fasta.amb:/var/lib/cwl/job979368791_bwa-mem/19.fasta.amb:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/19.fasta.pac:/var/lib/cwl/job979368791_bwa-mem/19.fasta.pac:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/HWI-ST1027_129_D0THKACXX.1_2.fastq:/var/lib/cwl/job979368791_bwa-mem/HWI-ST1027_129_D0THKACXX.1_2.fastq:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem/19.fasta.bwt:/var/lib/cwl/job979368791_bwa-mem/19.fasta.bwt:ro \
--volume=/home/example/arvados/doc/user/cwl/bwa-mem:/var/spool/cwl:rw \
--volume=/tmp/tmpgzyou9:/tmp:rw \
--workdir=/var/spool/cwl \
--read-only=true \
--log-driver=none \
--user=1001 \
--rm \
--env=TMPDIR=/tmp \
--env=HOME=/var/spool/cwl \
biodckr/bwa \
bwa \
mem \
-t \
1 \
-R \
'@RG ID:arvados_tutorial PL:illumina SM:HWI-ST1027_129' \
/var/lib/cwl/job979368791_bwa-mem/19.fasta \
/var/lib/cwl/job979368791_bwa-mem/HWI-ST1027_129_D0THKACXX.1_1.fastq \
/var/lib/cwl/job979368791_bwa-mem/HWI-ST1027_129_D0THKACXX.1_2.fastq > /home/example/arvados/doc/user/cwl/bwa-mem/HWI-ST1027_129_D0THKACXX.1_1.sam
[M::bwa_idx_load_from_disk] read 0 ALT contigs
[M::process] read 100000 sequences (10000000 bp)...
[M::mem_pestat] # candidate unique pairs for (FF, FR, RF, RR): (0, 4745, 1, 0)
[M::mem_pestat] skip orientation FF as there are not enough pairs
[M::mem_pestat] analyzing insert size distribution for orientation FR...
[M::mem_pestat] (25, 50, 75) percentile: (154, 181, 214)
[M::mem_pestat] low and high boundaries for computing mean and std.dev: (34, 334)
[M::mem_pestat] mean and std.dev: (185.63, 44.88)
[M::mem_pestat] low and high boundaries for proper pairs: (1, 394)
[M::mem_pestat] skip orientation RF as there are not enough pairs
[M::mem_pestat] skip orientation RR as there are not enough pairs
[M::mem_process_seqs] Processed 100000 reads in 9.848 CPU sec, 9.864 real sec
[main] Version: 0.7.12-r1039
[main] CMD: bwa mem -t 1 -R @RG ID:arvados_tutorial PL:illumina SM:HWI-ST1027_129 /var/lib/cwl/job979368791_bwa-mem/19.fasta /var/lib/cwl/job979368791_bwa-mem/HWI-ST1027_129_D0THKACXX.1_1.fastq /var/lib/cwl/job979368791_bwa-mem/HWI-ST1027_129_D0THKACXX.1_2.fastq
[main] Real time: 10.061 sec; CPU: 10.032 sec
Final process status is success
{
"aligned_sam": {
"size": 30738959,
"path": "/home/example/arvados/doc/user/cwl/bwa-mem/HWI-ST1027_129_D0THKACXX.1_1.sam",
"checksum": "sha1$0c668cca45fef02397bb5302880526d300ee4dac",
"class": "File"
}
}
</code></pre>
</notextile>
If you get the error @JavascriptException: Long-running script killed after 20 seconds.@ this may be due to the Dockerized Node.js engine taking too long to start. You may address this by installing Node.js locally (run @apt-get install nodejs@ on Debian or Ubuntu) or by specifying a longer timeout with the @--eval-timeout@ option. For example, run the workflow with @cwltool --eval-timeout=40@ for a 40-second timeout.
h2. Making workflows directly executable
You can make a workflow file directly executable (@cwl-runner@ should be an alias to @arvados-cwl-runner@) by adding the following line to the top of the file:
<notextile>
<pre><code>#!/usr/bin/env cwl-runner
</code></pre>
</notextile>
<notextile>
<pre><code>~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">./bwa-mem.cwl bwa-mem-input.yml</span>
arvados-cwl-runner 1.0.20160628195002, arvados-python-client 0.1.20160616015107, cwltool 1.0.20160629140624
2016-06-30 14:56:36 arvados.arv-run[27002] INFO: Upload local files: "bwa-mem.cwl"
2016-06-30 14:56:36 arvados.arv-run[27002] INFO: Uploaded to qr1hi-4zz18-h7ljh5u76760ww2
2016-06-30 14:56:40 arvados.cwl-runner[27002] INFO: Submitted job qr1hi-8i9sb-fm2n3b1w0l6bskg
2016-06-30 14:56:41 arvados.cwl-runner[27002] INFO: Job bwa-mem.cwl (qr1hi-8i9sb-fm2n3b1w0l6bskg) is Running
2016-06-30 14:57:12 arvados.cwl-runner[27002] INFO: Job bwa-mem.cwl (qr1hi-8i9sb-fm2n3b1w0l6bskg) is Complete
2016-06-30 14:57:12 arvados.cwl-runner[27002] INFO: Overall process status is success
{
"aligned_sam": {
"path": "keep:54325254b226664960de07b3b9482349+154/HWI-ST1027_129_D0THKACXX.1_1.sam",
"checksum": "sha1$0dc46a3126d0b5d4ce213b5f0e86e2d05a54755a",
"class": "File",
"size": 30738986
}
}
</code></pre>
</notextile>
You can even make an input file directly executable the same way with the following two lines at the top:
<notextile>
<pre><code>#!/usr/bin/env cwl-runner
cwl:tool: <span class="userinput">bwa-mem.cwl</span>
</code></pre>
</notextile>
<notextile>
<pre><code>~/arvados/doc/user/cwl/bwa-mem$ <span class="userinput">./bwa-mem-input.yml</span>
arvados-cwl-runner 1.0.20160628195002, arvados-python-client 0.1.20160616015107, cwltool 1.0.20160629140624
2016-06-30 14:56:36 arvados.arv-run[27002] INFO: Upload local files: "bwa-mem.cwl"
2016-06-30 14:56:36 arvados.arv-run[27002] INFO: Uploaded to qr1hi-4zz18-h7ljh5u76760ww2
2016-06-30 14:56:40 arvados.cwl-runner[27002] INFO: Submitted job qr1hi-8i9sb-fm2n3b1w0l6bskg
2016-06-30 14:56:41 arvados.cwl-runner[27002] INFO: Job bwa-mem.cwl (qr1hi-8i9sb-fm2n3b1w0l6bskg) is Running
2016-06-30 14:57:12 arvados.cwl-runner[27002] INFO: Job bwa-mem.cwl (qr1hi-8i9sb-fm2n3b1w0l6bskg) is Complete
2016-06-30 14:57:12 arvados.cwl-runner[27002] INFO: Overall process status is success
{
"aligned_sam": {
"path": "keep:54325254b226664960de07b3b9482349+154/HWI-ST1027_129_D0THKACXX.1_1.sam",
"checksum": "sha1$0dc46a3126d0b5d4ce213b5f0e86e2d05a54755a",
"class": "File",
"size": 30738986
}
}
</code></pre>
</notextile>