Cloud Build is a service that applies one or more container images in series to some initial set of input files and often generating some artifacts, often (not always) another container image, often some source code that was initially submitted that the service builds into a container image.
Cloud Build is somewhat analogous to e.g. Linux pipelines where some input is transformed by piping data through a series of commands: f | g | h | .... Alternatively you may think of it as composited functions: h(g(f(x))).
Cloud Build is described (and named) as a service to build (code into containers) but, as you know, actually the steps may be any container image and often these have side-effects such as deploying container images to other services e.g. Cloud Run.
Cloud Build is much more general-purpose than Google advertises it. Google limits its scope in its documentation to a cloud-based service to build software.
When you run gcloud builds submit... you provide some source code and either a Dockerfile or a configuration file. The former is a simple case of the second, a configuration file containing a single step that runs docker build....
Configuration files (YAML) list a series of container images with parameters that are run in series. Initially Cloud Build copies a designated source (can be the current directory) to a Compute Engine VM (created by the service) as a directory (that's automatically mounted into each container) as /workspace.
Containers (defined as steps in the configuration file) may operate on this file system (e.g. compline code, validate files, anything that you can do in a container). Often, in conclusion, config files store containers that have been created in e.g. Container Registry.
Solving Quadratic equations with Cloud Build
Cloud Build can be confusing to newcomers. In a spirit of fun and as a way to show that Cloud Build is quite general-purpose, here's a Rube Goldberg machine written in Cloud Build that solves quadratic equations:
For the following cloudbuild.yaml:
steps:
- name: busybox
args:
- ash
- -c
- 'echo "Quadratic: $(cat a)x²+$(cat b)x+$(cat c)s=0"'
- name: busybox
args:
- ash
- -c
- 'echo "$(cat b) * $(cat b)" | bc -l > b2'
- name: busybox
args:
- ash
- -c
- 'echo "4 * $(cat a) * $(cat c)" | bc -l > 4ac'
- name: busybox
args:
- ash
- -c
- 'echo "$(cat b2) - $(cat 4ac)" | bc -l > b2-4ac'
- name: busybox
args:
- ash
- -c
- 'echo "sqrt($(cat b2-4ac))" | bc -l > sqrt'
- name: busybox
args:
- ash
- -c
- 'echo "-($(cat b)) + $(cat sqrt)" | bc -l > add'
- name: busybox
args:
- ash
- -c
- 'echo "-($(cat b)) - $(cat sqrt)" | bc -l > sub'
- name: busybox
args:
- ash
- -c
- 'echo "2 * $(cat a)" | bc -l > 2a'
- name: busybox
args:
- ash
- -c
- 'echo "$(cat add)/$(cat 2a)" | bc -l > root1'
- name: busybox
args:
- ash
- -c
- 'echo "$(cat sub)/$(cat 2a)" | bc -l > root2'
- name: busybox
args:
- ash
- -c
- 'echo "Roots are: $(cat root1); $(cat root2)"'
It expects 3 files (a, b, c) in ${PWD} containing the values of ax²+bx+c=0. So, for 8x²-10x+3:
echo "8" > a
echo "-10" > b
echo "3" > c
You can run it with:
gcloud builds submit ${PWD} \
--config=./cloudbuild.yaml \
--project=${PROJECT}
Explanation Rube Goldberg Cloud Build machine for solving Quadratic equations
