Pipelines¶
Spack provides commands that support generating and running automated build
pipelines designed for Gitlab CI. At the highest level it works like this:
provide a spack environment describing the set of packages you care about,
and include within that environment file a description of how those packages
should be mapped to Gitlab runners. Spack can then generate a .gitlab-ci.yml
file containing job descriptions for all your packages that can be run by a
properly configured Gitlab CI instance. When run, the generated pipeline will
build and deploy binaries, and it can optionally report to a CDash instance
regarding the health of the builds as they evolve over time.
Getting started with pipelines¶
It is fairly straightforward to get started with automated build pipelines. At a minimum, you’ll need to set up a Gitlab instance (more about Gitlab CI here) and configure at least one runner. Then the basic steps for setting up a build pipeline are as follows:
Create a repository on your gitlab instance
Add a
spack.yaml
at the root containing your pipeline environment (see below for details)Add a
.gitlab-ci.yml
at the root containing a single job, similar to this one:pipeline-job: tags: - <custom-tag> ... script: - spack ci start
Add any secrets required by the CI process to environment variables using the CI web ui
Push a commit containing the
spack.yaml
and.gitlab-ci.yml
mentioned above to the gitlab repository
The <custom-tag>
, above, is used to pick one of your configured runners,
while the use of the spack ci start
command implies that runner has an
appropriate version of spack installed and configured for use. Of course, there
are myriad ways to customize the process. You can configure CDash reporting
on the progress of your builds, set up S3 buckets to mirror binaries built by
the pipeline, clone a custom spack repository/ref for use by the pipeline, and
more.
While it is possible to set up pipelines on gitlab.com, the builds there are limited to 60 minutes and generic hardware. It is also possible to hook up Gitlab to Google Kubernetes Engine (GKE) or Amazon Elastic Kubernetes Service (EKS), though those topics are outside the scope of this document.
Spack commands supporting pipelines¶
Spack provides a command ci with sub-commands for doing various things related
to automated build pipelines. All of the spack ci ...
commands must be run
from within a environment, as each one makes use of the environment for different
purposes. Additionally, some options to the commands (or conditions present in
the spack environment file) may require particular environment variables to be
set in order to function properly. Examples of these are typically secrets
needed for pipeline operation that should not be visible in a spack environment
file. These environment variables are described in more detail
Environment variables affecting pipeline operation.
spack ci
¶
Super-command for functionality related to generating pipelines and executing pipeline jobs.
spack ci start
¶
Currently this command is a short-cut to first run spack ci generate
, followed
by spack ci pushyaml
.
spack ci generate
¶
Concretizes the specs in the active environment, stages them (as described in
Summary of .gitlab-ci.yml generation algorithm), and writes the resulting .gitlab-ci.yml
to disk.
spack ci pushyaml
¶
Generates a commit containing the generated .gitlab-ci.yml
and pushes it to a
DOWNSTREAM_CI_REPO
, which is frequently the same repository. The branch
created has the same name as the current branch being tested, but has multi-ci-
prepended to the branch name. Once Gitlab CI has full support for dynamically
defined workloads, this command will be deprecated.
spack ci rebuild
¶
This sub-command is responsible for ensuring a single spec from the release
environment is up to date on the remote mirror configured in the environment,
and as such, corresponds to a single job in the .gitlab-ci.yml
file.
A pipeline-enabled spack environment¶
Here’s an example of a spack environment file that has been enhanced with sections desribing a build pipeline:
spack:
definitions:
- pkgs:
- readline@7.0
- compilers:
- '%gcc@5.5.0'
- oses:
- os=ubuntu18.04
- os=centos7
specs:
- matrix:
- [$pkgs]
- [$compilers]
- [$oses]
mirrors:
cloud_gitlab: https://mirror.spack.io
gitlab-ci:
mappings:
- match:
- os=ubuntu18.04
runner-attributes:
tags:
- spack-k8s
image: spack/spack_builder_ubuntu_18.04
- match:
- os=centos7
runner-attributes:
tags:
- spack-k8s
image: spack/spack_builder_centos_7
cdash:
build-group: Release Testing
url: https://cdash.spack.io
project: Spack
site: Spack AWS Gitlab Instance
Hopefully, the definitions
, specs
, mirrors
, etc. sections are already
familiar, as they are part of spack Environments. So let’s take a more
in-depth look some of the pipeline-related sections in that environment file
that might not be as familiar.
The gitlab-ci
section is used to configure how the pipeline workload should be
generated, mainly how the jobs for building specs should be assigned to the
configured runners on your instance. Each entry within the list of mappings
corresponds to a known gitlab runner, where the match
section is used
in assigning a release spec to one of the runners, and the runner-attributes
section is used to configure the spec/job for that particular runner.
There are other pipeline options you can configure within the gitlab-ci
section
as well. The bootstrap
section allows you to specify lists of specs from
your definitions
that should be staged ahead of the environment’s specs
(this
section is described in more detail below). The enable-artifacts-buildcache
key
takes a boolean and determines whether the pipeline uses artifacts to store and
pass along the buildcaches from one stage to the next (the default if you don’t
provide this option is False
). The enable-debug-messages
key takes a boolean
and allows you to choose whether the pipeline build jobs are run as spack -d ci rebuild
or just spack ci rebuild
(the default is not to enable debug messages). The
final-stage-rebuild-index
section controls whether an extra job is added to the
end of your pipeline (in a stage by itself) which will regenerate the mirror’s
buildcache index. Under normal operation, each pipeline job that rebuilds a package
will re-generate the mirror’s buildcache index after the buildcache entry for that
job has been created and pushed to the mirror. Since jobs in the same stage can run in
parallel, there is the possibility that at the end of some stage, the index may not
reflect all the binaries in the buildcache. Adding the final-stage-rebuild-index
section ensures that at the end of the pipeline, the index will be in sync with the
binaries on the mirror. If the mirror lives in an S3 bucket, this job will need to
run on a machine with the Python boto3
module installed, and consequently the
final-stage-rebuild-index
needs to specify a list of tags
to pick a runner
satisfying that condition. It can also take an image
key so Docker executor type
runners can pick the right image for the index regeneration job.
The optional cdash
section provides information that will be used by the
spack ci generate
command (invoked by spack ci start
) for reporting
to CDash. All the jobs generated from this environment will belong to a
“build group” within CDash that can be tracked over time. As the release
progresses, this build group may have jobs added or removed. The url, project,
and site are used to specify the CDash instance to which build results should
be reported.
Assignment of specs to runners¶
The mappings
section corresponds to a list of runners, and during assignment
of specs to runners, the list is traversed in order looking for matches, the
first runner that matches a release spec is assigned to build that spec. The
match
section within each runner mapping section is a list of specs, and
if any of those specs match the release spec (the spec.satisfies()
method
is used), then that runner is considered a match.
Configuration of specs/jobs for a runner¶
Once a runner has been chosen to build a release spec, the runner-attributes
section provides information determining details of the job in the context of
the runner. The runner-attributes
section must have a tags
key, which
is a list containing at least one tag used to select the runner from among the
runners known to the gitlab instance. For Docker executor type runners, the
image
key is used to specify the Docker image used to build the release spec
(and could also appear as a dictionary with a name
specifying the image name,
as well as an entrypoint
to override whatever the default for that image is).
For other types of runners the variables
key will be useful to pass any
information on to the runner that it needs to do its work (e.g. scheduler
parameters, etc.).
Summary of .gitlab-ci.yml
generation algorithm¶
All specs yielded by the matrix (or all the specs in the environment) have their
dependencies computed, and the entire resulting set of specs are staged together
before being run through the gitlab-ci/mappings
entries, where each staged
spec is assigned a runner. “Staging” is the name we have given to the process
of figuring out in what order the specs should be built, taking into consideration
Gitlab CI rules about jobs/stages. In the staging process the goal is to maximize
the number of jobs in any stage of the pipeline, while ensuring that the jobs in
any stage only depend on jobs in previous stages (since those jobs are guaranteed
to have completed already). As a runner is determined for a job, the information
in the runner-attributes
is used to populate various parts of the job
description that will be used by Gitlab CI. Once all the jobs have been assigned
a runner, the .gitlab-ci.yml
is written to disk.
The short example provided above would result in the readline
, ncurses
,
and pkgconf
packages getting staged and built on the runner chosen by the
spack-k8s
tag. In this example, we assume the runner is a Docker executor
type runner, and thus certain jobs will be run in the centos7
container,
and others in the ubuntu-18.04
container. The resulting .gitlab-ci.yml
will contain 6 jobs in three stages. Once the jobs have been generated, the
presence of a SPACK_CDASH_AUTH_TOKEN
environment variable during the
spack ci generate
command would result in all of the jobs being put in a
build group on CDash called “Release Testing” (that group will be created if
it didn’t already exist).
Optional compiler bootstrapping¶
Spack pipelines also have support for bootstrapping compilers on systems that
may not already have the desired compilers installed. The idea here is that
you can specify a list of things to bootstrap in your definitions
, and
spack will guarantee those will be installed in a phase of the pipeline before
your release specs, so that you can rely on those packages being available in
the binary mirror when you need them later on in the pipeline. At the moment
the only viable use-case for bootstrapping is to install compilers.
Here’s an example of what bootstrapping some compilers might look like:
spack:
definitions:
- compiler-pkgs:
- 'llvm+clang@6.0.1 os=centos7'
- 'gcc@6.5.0 os=centos7'
- 'llvm+clang@6.0.1 os=ubuntu18.04'
- 'gcc@6.5.0 os=ubuntu18.04'
- pkgs:
- readline@7.0
- compilers:
- '%gcc@5.5.0'
- '%gcc@6.5.0'
- '%gcc@7.3.0'
- '%clang@6.0.0'
- '%clang@6.0.1'
- oses:
- os=ubuntu18.04
- os=centos7
specs:
- matrix:
- [$pkgs]
- [$compilers]
- [$oses]
exclude:
- '%gcc@7.3.0 os=centos7'
- '%gcc@5.5.0 os=ubuntu18.04'
gitlab-ci:
bootstrap:
- name: compiler-pkgs
compiler-agnostic: true
mappings:
# mappings similar to the example higher up in this description
...
In the example above, we have added a list to the definitions
called
compiler-pkgs
(you can add any number of these), which lists compiler packages
we want to be staged ahead of the full matrix of release specs (which consists
only of readline in our example). Then within the gitlab-ci
section, we
have added a bootstrap
section, which can contain a list of items, each
referring to a list in the definitions
section. These items can either
be a dictionary or a string. If you supply a dictionary, it must have a name
key whose value must match one of the lists in definitions and it can have a
compiler-agnostic
key whose value is a boolean. If you supply a string,
then it needs to match one of the lists provided in definitions
. You can
think of the bootstrap list as an ordered list of pipeline “phases” that will
be staged before your actual release specs. While this introduces another
layer of bottleneck in the pipeline (all jobs in all stages of one phase must
complete before any jobs in the next phase can begin), it also means you are
guaranteed your bootstrapped compilers will be available when you need them.
The compiler-agnostic
key can be provided with each item in the
bootstrap list. It tells the spack ci generate
command that any jobs staged
from that particular list should have the compiler removed from the spec, so
that any compiler available on the runner where the job is run can be used to
build the package.
When including a bootstrapping phase as in the example above, the result is that
the bootstrapped compiler packages will be pushed to the binary mirror (and the
local artifacts mirror) before the actual release specs are built. In this case,
the jobs corresponding to subsequent release specs are configured to
install_missing_compilers
, so that if spack is asked to install a package
with a compiler it doesn’t know about, it can be quickly installed from the
binary mirror first.
Since bootstrapping compilers is optional, those items can be left out of the environment/stack file, and in that case no bootstrapping will be done (only the specs will be staged for building) and the runners will be expected to already have all needed compilers installed and configured for spack to use.
Using a custom spack in your pipeline¶
If your runners will not have a version of spack ready to invoke, or if for some
other reason you want to use a custom version of spack to run your pipelines,
this can be accomplished fairly simply. First, create CI environment variables
containing the url and branch/tag you want to clone (calling them, for example,
SPACK_REPO
and SPACK_REF
), use them to clone spack in your pre-ci
before_script
, and finally pass those same values along to the workload
generation process via the spack-repo
and spack-ref
cli args. Here’s
an example:
pipeline-job:
tags:
- <some-other-tag>
before_script:
- git clone ${SPACK_REPO} --branch ${SPACK_REF}
- . ./spack/share/spack/setup-env.sh
script:
- spack ci start --spack-repo ${SPACK_REPO} --spack-ref ${SPACK_REF} <...args>
after_script:
- rm -rf ./spack
If the spack ci start
command receives those extra command line arguments,
then it adds similar before_script
and after_script
sections for each of
the spack ci rebuild
jobs it generates (cloning and sourcing a custom
spack in the before_script
and removing it again in the after_script
).
This gives you control over the version of spack used when the rebuild jobs
are actually run on the gitlab runner.
Environment variables affecting pipeline operation¶
Certain secrets and some other information should be provided to the pipeline infrastructure via environment variables, usually for reasons of security, but in some cases to support other pipeline use cases such as PR testing. The environment variables used by the pipeline infrastructure are described here.
AWS_ACCESS_KEY_ID¶
Needed when binary mirror is an S3 bucket.
AWS_SECRET_ACCESS_KEY¶
Needed when binary mirror is an S3 bucket.
S3_ENDPOINT_URL¶
Needed when binary mirror is an S3 bucket that is not on AWS.
CDASH_AUTH_TOKEN¶
Needed in order to report build groups to CDash.
SPACK_SIGNING_KEY¶
Needed to sign/verify binary packages from the remote binary mirror.
DOWNSTREAM_CI_REPO¶
Needed until Gitlab CI supports dynamic job generation. Can contain connection credentials, and could be the same repository or a different one.