Case 1)
jenkins-master test:
cloud:
Name: gce
Project: <project>
Instance Cap: (1|3|8)
Service Account Credentials: <account>
Templates:
Name Prefix: template-test
Descriptios: <some description>
Launch Timeout: 300
Node Retention Time: 6
Usage: Only build jobs with label expressions matching this node
Labels: gcp-tmp-test
Run as user: jenkins
RegionL: europe-west-1
Zone: europe-west1-b
Machine Type: (n1-standatd-32|any)
Number of Executors: 4
Preemptible: no
Startup script: <no>
GPUs: no
Networking:
Network: default
Subnetwork: default
Network tags: jenkins slave
External IP?: yes
Boot Disk:
Image project: <project>
Image name: <name>
Disk Type: pd-standard
Size: 150
Delete on termination?: yes
IAM: <bot_1>@<project>.iam.gserviceaccount.com
Name Prefix: slave-gce
Descriptios: <some description>
Launch Timeout: 300
Node Retention Time: 6
Usage: Only build jobs with label expressions matching this node
Labels: gcp-tmp-test-2
Run as user: jenkins
RegionL: europe-west-1
Zone: europe-west1-b
Machine Type: (n1-standatd-32|any)
Number of Executors: 4
Preemptible: no
Startup script: <no>
GPUs: no
Networking:
Network: default
Subnetwork: default
Network tags: jenkins slave
External IP?: yes
Boot Disk:
Image project: <project>
Image name: <name>
Disk Type: pd-standard
Size: 150
Delete on termination?: yes
IAM: <bot_1>@<project>.iam.gserviceaccount.com

Jobs:
1) Freestyle project
Name: it-gce-test
Restrict where this project can be run: gcp-tmp-test
build shell:
"""
uname -a
ps -ef
df -h
docker ps
docker pull ubuntu
docker images
ls -la /tmp
cat /etc/passwd
"""
2) Freestyle project
Name: it-gce-test-double
Restrict where this project can be run: gcp-tmp-test-2
build shell:
"""
uname -a
ps -ef
df -h
docker ps
docker pull ubuntu
docker images
ls -la /tmp
cat /etc/passwd
"""

Steps:

• Run Job it-gce-test
• Created jenkins slave template-test-******
• Created one instance in GCE template-test-******
• Build result: success.
• slave template-test-****** still up

• Run Job it-gce-test-double
• 3 minutes nothing to change. 1 job in queue
• slave template-test-****** removed
• created jenkins slave slave-gce-******
• build result: success.
• Over 50 running instances in GCE with name: slave-gce-******

Case 2)
The same configuration, as a case 1, but i created 2 cluds with 1 template for each.
Nothing to change. This plugin create only 1 jenkins slave and the second can't be created before first jenkins slave don't removed. But in GCE created instances without control.

Case 3) I create 1 cloud in production jenkins and one cloud in test jenkins. One instance template for each cloud.
Production jenkins master.
Production cloud:
cloud:
Name: gce
Project: <project>
Instance Cap: (1|3|8)
Service Account Credentials: <account>
Templates:
Name Prefix: template-prod
Descriptios: <some description>
Launch Timeout: 300
Node Retention Time: 6
Usage: Only build jobs with label expressions matching this node
Labels: gcp-tmp-test
Run as user: jenkins
RegionL: europe-west-1
Zone: europe-west1-b
Machine Type: (n1-standatd-32|any)
Number of Executors: 4
Preemptible: no
Startup script: <no>
GPUs: no
Networking:
Network: default
Subnetwork: default
Network tags: jenkins slave
External IP?: yes
Boot Disk:
Image project: <project>
Image name: <name>
Disk Type: pd-standard
Size: 150
Delete on termination?: yes
IAM: <bot_1>@<project>.iam.gserviceaccount.com

Test jenkins master
Test cloud:
cloud:
Name: gce
Project: <project>
Instance Cap: (1|3|8)
Service Account Credentials: <account>
Templates:
Name Prefix: template-test
Descriptios: <some description>
Launch Timeout: 300
Node Retention Time: 6
Usage: Only build jobs with label expressions matching this node
Labels: gcp-tmp-test
Run as user: jenkins
RegionL: europe-west-1
Zone: europe-west1-b
Machine Type: (n1-standatd-32|any)
Number of Executors: 4
Preemptible: no
Startup script: <no>
GPUs: no
Networking:
Network: default
Subnetwork: default
Network tags: jenkins slave
External IP?: yes
Boot Disk:
Image project: <project>
Image name: <name>
Disk Type: pd-standard
Size: 150
Delete on termination?: yes
IAM: <bot_1>@<project>.iam.gserviceaccount.com

I used one Google Project and One Service account for test and production cloud

Jobs:
production:
Freestyle project
Name: it-gce-test
Restrict where this project can be run: gcp-tmp-test
build shell:
"""
uname -a
ps -ef
df -h
docker ps
docker pull ubuntu
docker images
ls -la /tmp
cat /etc/passwd
"""

Test:
Freestyle project
Name: it-gce-test
Restrict where this project can be run: gcp-tmp-test
build shell:
"""
uname -a
ps -ef
df -h
docker ps
docker pull ubuntu
docker images
ls -la /tmp
cat /etc/passwd
"""

Steps:

• Run Job it-gce-test on production and test jenkins
• Created jenkins slave template-test-****** on test jenkins
• Created jenkins slave template-prod-****** on production jenkins

• Created one instance in GCE template-test-****** in GCE
• Created one instance in GCE template-prod-****** in GCE

• Build results: success.
• slave template-test-****** up 6 minuts and destroyed with GCE instance
• slave template-prod-****** up 6 minuts and destroyed with GCE instance

I think the problem is in jenkins slaves. When one slave created by the plugin is upped, the second one can't created. But the second creates unlimited instances in the GCE.
In this moment we can use only 1 template per jenkins master. Please fix this problem.