CloudBuild jobs not executed in parallel - google-cloud-build

Question

I am learning CloudBuild and understand that I can use waitFor to influence the order in which my build runs. job1 includes some sleep time to simulate a long running job. job2 just echos something. done waits for job1 & job2. So I created a test build like this: I have a package.json
{
"scripts": {
"job1": "echo \"[job1] Starting\" && sleep 5 && echo \"[job1] ...\" && sleep 2 && echo \"[job1] Done\" && exit 0",
"job2": "echo \"[job2] Hello from NPM\" && exit 0",
"done": "echo \"DONE DONE DONE!\" && exit 0"
},
}
Job 1 simulates a long running job, where I was hopping job 2 will execute in parallel. But seems like the output shows its not. Does CloudBuild run 1 step at a time only?
cloudbuild.yaml
steps:
- name: 'gcr.io/cloud-builders/npm'
args: ['run', 'job1']
id: 'job1'
- name: 'gcr.io/cloud-builders/npm'
args: ['run', 'job2']
id: 'job2'
- name: 'gcr.io/cloud-builders/npm'
args: ['run', 'done']
waitFor: ['job1', 'job2']
Output
Operation completed over 1 objects/634.0 B.
BUILD
Starting Step #0 - "job1"
Step #0 - "job1": Already have image (with digest): gcr.io/cloud-builders/npm
Step #0 - "job1":
Step #0 - "job1": > learn-gcp#1.0.0 job1 /workspace
Step #0 - "job1": > echo "[job1] Starting" && sleep 5 && echo "[job1] ..." && sleep 2 && echo "[job1] Done" && exit 0
Step #0 - "job1":
Step #0 - "job1": [job1] Starting
Step #0 - "job1": [job1] ...
Step #0 - "job1": [job1] Done
Finished Step #0 - "job1"
Starting Step #1 - "job2"
Step #1 - "job2": Already have image (with digest): gcr.io/cloud-builders/npm
Step #1 - "job2":
Step #1 - "job2": > learn-gcp#1.0.0 job2 /workspace
Step #1 - "job2": > echo "[job2] Hello from NPM" && exit 0
Step #1 - "job2":
Step #1 - "job2": [job2] Hello from NPM
Finished Step #1 - "job2"
Starting Step #2
Step #2: Already have image (with digest): gcr.io/cloud-builders/npm
Step #2:
Step #2: > learn-gcp#1.0.0 done /workspace
Step #2: > echo "DONE DONE DONE!" && exit 0
Step #2:
Step #2: DONE DONE DONE!
Finished Step #2
PUSH
DONE

Answer 1

If you wanted the job2 to be executed concurrently with job1 you should have added the line
waitFor: ['-'] in your cloudbuild.yaml, immediatly after job2. As it is stated in the official documentation:
If no values are provided for waitFor, the build step waits for all prior build steps in the build request to complete successfully before running.
To run a build step immediately at build time, use - in the waitFor
field.
The order of the build steps in the steps field relates to the order
in which the steps are executed. Steps will run serially or
concurrently based on the dependencies defined in their waitFor
fields.
In the documentation is, also an example on how to run two jobs in parallel.
In case you want job2 to run allong with job1 you should have something like this:
steps:
- name: 'gcr.io/cloud-builders/npm'
args: ['run', 'job1']
id: 'job1'
- name: 'gcr.io/cloud-builders/npm'
args: ['run', 'job2']
id: 'job2'
waitFor: ['-'] # The '-' indicates that this step begins immediately.
- name: 'gcr.io/cloud-builders/npm'
args: ['run', 'done']
waitFor: ['job1', 'job2']
Also note that the maximum number of concurent builds you can use is ten.