An introduction to using dxCompiler, a tool for compiling WDL and CWL workflows on the DNAnexus platform

dxCompiler is a tool for compiling pipelines written in the Workflow Description Language (WDL) and the Common Workflow Language (CWL) to equivalent workflows on the DNAnexus platform.

Below we introduce a few use cases for dxCompiler. This tool can be downloaded from the dxCompiler Github repository, which also contains more advanced options including DNAnexus extensions and integration with private docker repositories.

dxCompiler Setup

For information on how to set up dxCompiler, see instructions on the dxCompiler Github page.

WDL Example

Validating a Workflow

dxCompiler uses wdlTools, a parser that adheres strictly to the WDL specifications. Most of the problematic automatic type conversions that are allowed by some other WDL runtime engines are not allowed by dxCompiler. Please use the command line tools in wdlTools (e.g. check and lint) to validate your WDL files before trying to compile them with dxCompiler.

Compiling and Running a Workflow

The bam_chrom_counter workflow is written in WDL. Task slice_bam splits a bam file into an array of sub-files. Task count_bam counts the number of alignments on a bam file. The workflow takes an input bam file, calls slice_bam to split it into chromosomes, and calls count_bam in parallel on each chromosome. The results comprise a bam index file, and an array with the number of reads per chromosome.

version 1.0

workflow bam_chrom_counter {
    input {
        File bam

    call slice_bam {
        input : bam = bam
    scatter (slice in slice_bam.slices) {
        call count_bam {
            input: bam = slice
    output {
        File bai = slice_bam.bai
        Array[Int] count = count_bam.count

task slice_bam {
    input {
        File bam
        Int num_chrom = 22
    command <<<
    set -ex
    samtools index ~{bam}
    mkdir slices/
    for i in `seq ~{num_chrom}`; do
        samtools view -b ~{bam} -o slices/$i.bam $i
    runtime {
        docker: "quay.io/biocontainers/samtools:1.12--hd5e65b6_0"
    output {
        File bai = "~{bam}.bai"
        Array[File] slices = glob("slices/*.bam")

task count_bam {
    input {
        File bam

    command <<<
        samtools view -c ~{bam}
    runtime {
        docker: "quay.io/biocontainers/samtools:1.12--hd5e65b6_0"
    output {
        Int count = read_int(stdout())

From the command line, we can compile the workflow to the DNAnexus platform using the dxCompiler jar file.

$ java -jar dxCompiler.jar compile bam_chrom_counter.wdl \
    -project project-xxxx -folder /my/workflows/

This compiles the source WDL file to several platform objects in the specified DNAnexus project project-xxxx under folder /my/workflows/

  • A workflow bam_chrom_counter

  • Two applets that can be called independently: slice_bam, and count_bam

  • A few auxiliary applets that process workflow inputs, outputs, and launch the scatter.

You can review the structure of the compiled DNAnexus workflow using the describe dxCompiler subcommand. The output shows the generated DNAnexus workflows and applets in a tree that describes a caller/callee relationship.

$ java -jar dxCompiler.jar describe workflow-G3P0jFQ0Fgk3Z7855fqKyjPy --pretty
Workflow: bam_chrom_counter
├───App Inputs: common
├───App Task: slice_bam
├───App Fragment: scatter (slice in slice_bam.slices)
   └───App Task: count_bam
└───App Outputs: outputs

The generated workflow can be executed from the web UI (see instructions here) or via the DNAnexus command-line client. For example, to run the workflow with the input bam file project-BQbJpBj0bvygyQxgQ1800Jkk:file-FpQKQk00FgkGV3Vb3jJ8xqGV, use the following command:

dx run bam_chrom_counter \

Alternatively, you can also convert a Cromwell JSON format input file into a DNAnexus format when compiling the workflow. Then you can pass the DNAnexus input file to dx run using -f option as described in detail here.

$ java -jar dxCompiler.jar compile bam_chrom_counter.wdl \
   -project project-xxxx -folder /my/workflows/ \
   -inputs bam_chrom_counter_input.json
$ dx run bam_chrom_counter -f bam_chrom_counter_input.dx.json

After launching the workflow analysis, you can monitor it on the CLI following these instructions or from the UI as suggested here. CLI sessions shows the executed workflow:

$ dx find executions -n1
* bam_chrom_counter (done) analysis-G3P0kGj0Fgk8ZY0645QYZ9bB
│ demo-user 2022-03-01 11:42:59
├── * outputs (bam_chrom_counter_outputs:main) (done) job-G3P0kkQ0Fgk8ZY0645QYZ9bX
│     demo-user 2022-03-01 11:43:44 (runtime 0:00:42)
├── * scatter (slice in slice_bam.slices) (bam_chrom_counter_frag_stage-1:main) (done) job-G3P0kj00Fgk8ZY0645QYZ9bV
│   │ demo-user 2022-03-01 11:43:38 (runtime 0:00:46)
│   ├── collect_scatter (bam_chrom_counter_frag_stage-1:collect) (done) job-G3P1Gb80Fgk8gx406ppxVZX6
│   │   demo-user 2022-03-01 12:24:05 (runtime 0:00:42)
│   ├── count_bam dx://project-FZjPqzQ0Fgk1PPxyBJq4ZP0J:file-G3P1... (count_bam:main) (done) job-G3P1Gb80Fgk3ZjYx714yFZyQ
│   │   demo-user 2022-03-01 12:24:05 (runtime 0:01:31)
│   ├── count_bam dx://project-FZjPqzQ0Fgk1PPxyBJq4ZP0J:file-G3P1... (count_bam:main) (done) job-G3P1Gb00FgkBb45v7197QVb2
│   │   demo-user 2022-03-01 12:24:04 (runtime 0:01:34)
│   ├── count_bam dx://project-FZjPqzQ0Fgk1PPxyBJq4ZP0J:file-G3P1... (count_bam:main) (done) job-G3P1GZQ0Fgk0QBKp6pVZgzFg
│   │   demo-user 2022-03-01 12:24:01 (runtime 0:01:33)
│   ├── count_bam dx://project-FZjPqzQ0Fgk1PPxyBJq4ZP0J:file-G3P1... (count_bam:main) (done) job-G3P1GZ80Fgk9vFj26Vg599P4
│   │   demo-user 2022-03-01 12:24:01 (runtime 0:01:33)
│   └── count_bam dx://project-FZjPqzQ0Fgk1PPxyBJq4ZP0J:file-G3P1... (count_bam:main) (done) job-G3P1GZ80Fgk6VJ5v6kGYp5k9
│       demo-user 2022-03-01 12:24:01 (runtime 0:01:53)
├── * slice_bam (done) job-G3P0kfQ0Fgk8ZY0645QYZ9bQ
│     demo-user 2022-03-01 11:43:31 (runtime 0:37:14)
└── * common (bam_chrom_counter_common:main) (done) job-G3P0kZj0Fgk8ZY0645QYZ9bP
      demo-user 2022-03-01 11:43:25 (runtime 0:00:45)

The snapshot below shows what you will see from the UI when the workflow execution is completed:

CWL Example

Preprocessing a CWL Workflow

dxCompiler requires the source CWL file to be "packed" as a cwl.json file, which contains a single compound workflow with all the dependent processes included. Additionally, you may need to upgrade the version of your workflow to CWL v1.2.

We'll use the bam_chrom_counter CWL workflow similar to the WDL example above to illustrate upgrading, packing and running a CWL workflow. This workflow is written in CWL v1.0 and the top-level Workflow in bam_chrom_counter.cwl calls the two CommandLineTools in slice_bam.cwl and count_bam.cwl.

cwlVersion: v1.0
id: bam_chrom_counter
class: Workflow
- class: ScatterFeatureRequirement
- id: bam
  type: File
  # upload this local file to the platform and replace the path below with the DNAnexus URI "dx://project-xxx:file-yyyy"
  default: "path/to/my/input_bam"
- id: bai
  type: File
  outputSource: slice_bam/bai
- id: count
  type: int[]
  outputSource: count_bam/count
- id: slice_bam
  run: slice_bam.cwl
    bam: bam
  out: [bai, slices]
- id: count_bam
  run: count_bam.cwl
  scatter: bam
    bam: slice_bam/slices
  out: [count]
cwlVersion: v1.0
id: slice_bam
class: CommandLineTool
- id: bam
  type: File
- id: num_chrom
  default: 22
  type: int
- id: bai
  type: File
    glob: $(inputs.bam.basename).bai
- id: slices
  type: File[]
    glob: "slices/*.bam"
- class: InlineJavascriptRequirement
- class: ShellCommandRequirement
- class: DockerRequirement
  dockerPull: "quay.io/biocontainers/samtools:1.12--hd5e65b6_0"
- class: InitialWorkDirRequirement
  - entryname: slice_bam.sh
    entry: |-
      set -ex
      samtools index $1
      mkdir slices/
      for i in `seq $2`; do
          samtools view -b $1 -o slices/$i.bam $i
  - entry: $(inputs.bam)
baseCommand: ["sh", "slice_bam.sh"]
  - position: 0
    valueFrom: $(inputs.bam.basename)
  - position: 1
    valueFrom: $(inputs.num_chrom)
- class: NetworkAccess
  networkAccess: true
- class: LoadListingRequirement
  loadListing: deep_listing
cwlVersion: v1.0
id: count_bam
class: CommandLineTool
- class: InlineJavascriptRequirement
- class: ShellCommandRequirement
- class: DockerRequirement
  dockerPull: "quay.io/biocontainers/samtools:1.12--hd5e65b6_0"
- id: bam
  type: File
    position: 1
baseCommand: ["samtools", "view", "-c"]
- id: count
  type: int
    glob: stdout
    loadContents: true
    outputEval: "$(parseInt(self[0].contents))"
stdout: stdout
- class: NetworkAccess
  networkAccess: true
- class: LoadListingRequirement
  loadListing: deep_listingcount

Before compilation, follow the steps below to preprocess these CWL files:

  1. De-localize all local paths referenced in the CWL: if the CWL specifies a local path, e.g. a schema or a default value for a file-type input (like the default path "path/to/my/input_bam" for input bam in bam_chrom_counter.cwl), you need to upload this file to a DNAnexus project and then replace the local path in the CWL with its full DNAnexus URI, e.g. dx://project-XXX:file-YYY.

  2. Install cwl-upgrader and upgrade the CWL files to v1.2 (needed in this case as CWL files are in CWL v1.0):

    $ pip3 install cwl-upgrader
    # upgrade all dependent CWL files, which will be saved in the current working directory
    $ cd contrib/beginner_example
    $ cwl-upgrader cwl_v1.0/bam_chrom_counter.cwl cwl_v1.0/slice_bam.cwl cwl_v1.0/count_bam.cwl
  3. Install sbpack package and run the cwlpack command on the top-level workflow file to build a single packed bam_chrom_counter.cwl.json file containing the top level workflow and all the steps it depends on:

    $ pip3 install sbpack
    $ cwlpack --add-ids --json bam_chrom_counter.cwl > bam_chrom_counter.cwl.json

Validating a Workflow

dxCompiler compiles tools/workflows written according to the CWL v1.2 standard. You can use cwltool --validate to validate the packed CWL file you want to compile.

Compiling and Running a Workflow

Once it is upgraded and packed as suggested above, we can compile it as a DNAnexus workflow and run it.

$ java -jar dxCompiler.jar compile bam_chrom_counter.cwl.json -project project-xxxx -folder /my/workflows/
$ dx run bam_chrom_counter -istage-common.bam=project-BQbJpBj0bvygyQxgQ1800Jkk:file-FpQKQk00FgkGV3Vb3jJ8xqGV


  • WDL and CWL

    • Calls with missing arguments have limited support

    • All task and workflow names must be unique across the entire import tree

      • For example, if A.wdl imports B.wdl and A.wdl defines workflow foo, then B.wdl cannot have a workflow or task named foo

    • Subworkflows built from higher-level workflows are not intended to be used on their own

  • WDL only

    • Workflows with forward references (i.e. a variable referenced before it is declared) are not yet supported

    • The alternative workflow output syntax that has been deprecated since WDL draft2 is not supported

    • The call ... after syntax introduced in WDL 1.1 is not yet supported

  • CWL only

    • Calling native DNAnexus apps/applets in CWL workflow using dxni is not supported.

    • SoftwareRequirement and InplaceUpdateRequirement are not yet supported

    • Publishing a dxCompiler-generated workflow as a global workflow is not supported

    • Applet and job reuse is not supported

Help String

dxCompiler's capabilities are outlined in the dxCompiler's help string below.

$ java -jar dxCompiler.jar version
$ java -jar dxCompiler.jar help

java -jar dxCompiler.jar <action> <parameters> [options]

    Prints the dxCompiler version.

    Prints the current dxCompiler configuration.

  describe <DxWorkflow ID>
    Generate the JSON execution tree for a given DNAnexus workflow ID.
    The workflow needs to be have been previously compiled by dxCompiler.
      -pretty                Print exec tree in "pretty" text format instead of JSON.

  compile <WDL or CWL file>
    Compile a WDL or CWL file to a DNAnexus workflow or applet.
      -archive               Archive older versions of applets.
      -compileMode [IR, All]
                             Compilation mode - If not specified, the compilation
                             mode is "All" and the compiler will translate WDL or CWL
                             inputs into DNAnexus workflows and tasks.
                             Use "IR" if you only want to parse CWL or WDL files and
                             convert standard-formatted input files to DNAnexus JSON
                             input format without performing full compilation.
      -defaults <string>     JSON file with standard-formatted default values.
      -defaultInstanceType <string>
                             The default instance type to use for "helper" applets
                             that perform runtime evaluation of instance type
                             requirements. This instance type is also used when
                             the '-instanceTypeSelection dynamic' option is set.
                             This value is overriden by any defaults set in set in the
                             JSON file specified by '-extras'.
      -destination <string>  Full platform path (project:/folder).
      -execTree [json,pretty]
                             Print a JSON representation of the workflow.
      -extras <string>       JSON file with extra options (see documentation).
      -inputs <string>       JSON file with standard-formatted input values. May be
                             specified multiple times. A DNAnexus JSON input file is
                             generated for each standard input file.
      -instanceTypeSelection [static,dynamic]
                             Whether to select instance types at compile time for tasks with
                             runtime requirements that can all be statically evaluated
                             (the default "static" option), or to defer instance type
                             selection in such cases to runtime (the "dynamic" option).
                             Using static instance type selection can save time, but it
                             requires the same set of instances to be accessible during WDL/CWL
                             compilation and during the runtime of the generated applets and
                             workflows. Use the "dynamic" option if you plan on creating global
                             DNAnexus workflows or cloning the generated workflows between
                             DNAnexus organizations with different available instance types.
      -locked                Create a locked workflow. When running a locked workflow,
                             input values may only be specified for the top-level workflow.
      -leaveWorkflowsOpen    Leave created workflows open (otherwise they are closed).
      -p | -imports <string> Directory to search for imported WDL or CWL files. May be specified
                             multiple times.
      -projectWideReuse      Look for existing applets/workflows in the entire project
                             before generating new ones. The default search scope is the
                             target folder only.
      -reorg                 Reorganize workflow output files.
      -runtimeDebugLevel [0,1,2]
                             How much debug information to write to the job log at runtime.
                             Log the minimum (0), intermediate (1, the default), or all
                             debug information (2, for internal debugging).
      -separateOutputs       Store the output files of each call in a separate folder. The
                             default behavior is to put all outputs in the same folder.
      -streamFiles [all,none,perfile]
                             Whether to mount all files with dxfuse (do not use the
                             download agent), to mount no files with dxfuse (only use
                             download agent), or to respect the per-file settings in WDL
                             parameter_meta sections (default).
      -useManifests          Use manifest files for all workflow and applet inputs and
                             outputs. Implies -locked.
      -waitOnUpload          Whether to wait for each file upload to complete.

  dxni (WDL only)
    DNAnexus Native call Interface. Creates stubs for calling DNAnexus executables
    (apps/applets/workflows), and stores them as WDL tasks in a local file. Enables
    calling existing platform executables without modification.
      -apps [include,exclude,only]
                             Option 'include' includes both apps and applets, 'exclude'
                             excludes apps and generates applet stubs only, 'only'
                             generates app stubs only.
      -f | force             Delete any existing output file.
      -o <path>              Destination file for WDL task definitions (defaults to
      -path <string>         Name of a specific app or a path to a specific applet.
      -r | recursive         Search recursively for applets in the target folder.

Common options
    -folder <string>         Platform folder (defaults to '/').
    -project <string>        Platform project (defaults to currently selected project).
    -language <string> [ver] Which language to use? May be WDL or CWL. You can optionally
                             specify a version. Currently: i. WDL: draft-2, 1.0, and 1.1, and
                             ii. CWL: 1.2 are supported and WDL development is partially
                             supported. The default is to auto-detect the language from the
                             source file.
    -quiet                   Do not print warnings or informational outputs.
    -verbose                 Print detailed logging.
    -verboseKey <module>     Print verbose output only for a specific module. May be
                             specified multiple times.
    -logFile <path>          File to use for logging output; defaults to stderr.

A detailed description of the advanced dxCompiler features can be found in the public dxCompiler github repository here.

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