Why does my Selenium Grid in Azure Container Instances take the same time to execute tests regardless of number of nodes? - azure

Question

Because ACI doesn't support scaling, we deploy multiple container groups containing an Azure DevOps agent, a selenium grid hub and a selenium grid node. To try and speed things up I've tried to deploy the container groups with an additional node, identical to the first only being started on port 6666 instead of port 5555. I can see the two nodes register with the grid without issue but when I execute the same batch of tests with the additional node and without they take the exact same amount of time. How do I go about finding out what's going on here?
My ACI yaml:
apiVersion: 2018-10-01
location: australiaeast
properties:
containers:
- name: devops-agent
properties:
image: __AZUREDEVOPSAGENTIMAGE__
resources:
requests:
cpu: 0.5
memoryInGb: 1
environmentVariables:
- name: AZP_URL
value: __AZUREDEVOPSPROJECTURL__
- name: AZP_POOL
value: __AGENTPOOLNAME__
- name: AZP_TOKEN
secureValue: __AZUREDEVOPSAGENTTOKEN__
- name: SCREEN_WIDTH
value: "1920"
- name: SCREEN_HEIGHT
value: "1080"
volumeMounts:
- name: downloads
mountPath: /tmp/
- name: selenium-hub
properties:
image: selenium/hub:3.141.59-xenon
resources:
requests:
cpu: 1
memoryInGb: 1
ports:
- port: 4444
- name: chrome-node
properties:
image: selenium/node-chrome:3.141.59-xenon
resources:
requests:
cpu: 1
memoryInGb: 2
environmentVariables:
- name: HUB_HOST
value: localhost
- name: HUB_PORT
value: 4444
- name: SCREEN_WIDTH
value: "1920"
- name: SCREEN_HEIGHT
value: "1080"
volumeMounts:
- name: devshm
mountPath: /dev/shm
- name: downloads
mountPath: /home/seluser/downloads
- name: chrome-node-2
properties:
image: selenium/node-chrome:3.141.59-xenon
resources:
requests:
cpu: 1
memoryInGb: 2
environmentVariables:
- name: HUB_HOST
value: localhost
- name: HUB_PORT
value: 4444
- name: SCREEN_WIDTH
value: "1920"
- name: SCREEN_HEIGHT
value: "1080"
- name: SE_OPTS
value: "-port 6666"
volumeMounts:
- name: devshm
mountPath: /dev/shm
- name: downloads
mountPath: /home/seluser/downloads
osType: Linux
diagnostics:
logAnalytics:
workspaceId: __LOGANALYTICSWORKSPACEID__
workspaceKey: __LOGANALYTICSPRIMARYKEY__
volumes:
- name: devshm
emptyDir: {}
- name: downloads
emptyDir: {}
ipAddress:
type: Public
ports:
- protocol: tcp
port: '4444'
#==================== remove this section if not pulling images from private image registries ===============
imageRegistryCredentials:
- server: __IMAGEREGISTRYLOGINSERVER__
username: __IMAGEREGISTRYUSERNAME__
password: __IMAGEREGISTRYPASSWORD__
#========================================================================================================================
tags: null
type: Microsoft.ContainerInstance/containerGroups
When I run my tests locally against a docker selenium grid either from Visual Studio or via dotnet vstest, my tests run in parallel across all available nodes and complete in half the time.