Creating a Cross Project (or Account) Service Account in GCP Step-by-Step

Mike Elsmore

Mike Elsmore Nov 09, 2021

In Google Cloud Platform (GCP) it is common to have multiple projects for different environments (like dev, staging, prod, prod-team1, etc.). It is also a common use-case to have one set of credentials (service account) to access multiple accounts, For example:
  • Auditing: one service account with read-only access to all projects
  • Multi-project access/communication: one service in one project might need access/communicate to other services in different projects.
In this tutorial we will show you how to create one service account in GCP that can access multiple projects either under the same organization/account or even completely different accounts (for AWS users this is the GCP's assume role equivalent).

How do you set up a Service Account in GCP?

Assuming you’ve got your project setup (we are going to use Project A & Project B to test all this), you’ll want to navigate to Project A and then do the following steps:
  1. Within the IAM & Admin menu select Service Accounts
    Service Accounts is under the IAM & Admin menu
  3. Fill in the Service Accounts details, as it’s going to be used cross-projects make sure it’s clearly defined as such (you will be using the Service account ID later). Then select CREATE AND CONTINUE
    Fill in all the descriptive details for the account
  4. Now apply the permissions you want this Service Account to have, I’m using the Viewer permission, you can also add any conditions to the permissions
    Select the level of permissions for the service account
  5. Once you have applied all your desired permissions to the Service Account select CONTINUE
    Click CONTINUE to move to the next step
  6. If you’d like to grant specific users access to this Service Account (for modification or to see what it’s doing) you can add those users here
    Grant specific users access to the service account, this is optional
  7. After adding any users you wish to grant access, select DONE and you should be sent to a screen with the Service Account and it’s status etc
    List of your service accounts

How do we grant it access to other projects?

Once we have a working Service Account, we now have to go through a slightly different process to add it to other projects.
  1. Firstly, using the project navigation in the top menu select your second project. In my case this is Project B
    Moving to the second project
  2. Like before we need to select IAM & Admin from the menu, be this time we select IAM
    Go to the IAM under the IAM & Admin menu
  3. Once here simply select +ADD
    Select +ADD
  4. From this new menu, you will need to use the Service account ID from the previous flow of creating the Service Account
    Use the Service account ID from creating the service account
  5. And add the role you want to have assigned to the Service Account within this Project, I’m going with Viewer again
    Select the role with permissions for the account inside this project
  6. After applying all the roles and permissions the Service Account needs, click SAVE
    Select SAVE to complete the process
  7. After the policy has updated, you’ll be able to see your user in the IAM list
    Once saved the Service account is listed


And that’s it, your Service Account created in Project A now has access to both Project A and Project B, enjoy.
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