Manage GCP Backend Bucket IAM Access

The gcp:compute/backendBucketIamMember:BackendBucketIamMember resource, part of the Pulumi GCP provider, manages IAM permissions for Compute Engine backend buckets by adding individual members to roles. This guide focuses on three approaches to IAM management and when to use authoritative vs non-authoritative permission grants.

GCP provides three related resources for managing backend bucket IAM: BackendBucketIamPolicy (replaces entire policy), BackendBucketIamBinding (manages all members for one role), and BackendBucketIamMember (adds individual members). The examples are intentionally small. Combine them with your own backend bucket infrastructure and access requirements.

Replace the entire IAM policy for a backend bucket

When you need complete control over who can access a backend bucket, BackendBucketIamPolicy sets the entire IAM policy at once.

import * as pulumi from "@pulumi/pulumi";
import * as gcp from "@pulumi/gcp";

const admin = gcp.organizations.getIAMPolicy({
    bindings: [{
        role: "roles/viewer",
        members: ["user:jane@example.com"],
    }],
});
const policy = new gcp.compute.BackendBucketIamPolicy("policy", {
    project: imageBackend.project,
    name: imageBackend.name,
    policyData: admin.then(admin => admin.policyData),
});

import pulumi
import pulumi_gcp as gcp

admin = gcp.organizations.get_iam_policy(bindings=[{
    "role": "roles/viewer",
    "members": ["user:jane@example.com"],
}])
policy = gcp.compute.BackendBucketIamPolicy("policy",
    project=image_backend["project"],
    name=image_backend["name"],
    policy_data=admin.policy_data)

package main

import (
	"github.com/pulumi/pulumi-gcp/sdk/v9/go/gcp/compute"
	"github.com/pulumi/pulumi-gcp/sdk/v9/go/gcp/organizations"
	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
)

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		admin, err := organizations.LookupIAMPolicy(ctx, &organizations.LookupIAMPolicyArgs{
			Bindings: []organizations.GetIAMPolicyBinding{
				{
					Role: "roles/viewer",
					Members: []string{
						"user:jane@example.com",
					},
				},
			},
		}, nil)
		if err != nil {
			return err
		}
		_, err = compute.NewBackendBucketIamPolicy(ctx, "policy", &compute.BackendBucketIamPolicyArgs{
			Project:    pulumi.Any(imageBackend.Project),
			Name:       pulumi.Any(imageBackend.Name),
			PolicyData: pulumi.String(admin.PolicyData),
		})
		if err != nil {
			return err
		}
		return nil
	})
}

using System.Collections.Generic;
using System.Linq;
using Pulumi;
using Gcp = Pulumi.Gcp;

return await Deployment.RunAsync(() => 
{
    var admin = Gcp.Organizations.GetIAMPolicy.Invoke(new()
    {
        Bindings = new[]
        {
            new Gcp.Organizations.Inputs.GetIAMPolicyBindingInputArgs
            {
                Role = "roles/viewer",
                Members = new[]
                {
                    "user:jane@example.com",
                },
            },
        },
    });

    var policy = new Gcp.Compute.BackendBucketIamPolicy("policy", new()
    {
        Project = imageBackend.Project,
        Name = imageBackend.Name,
        PolicyData = admin.Apply(getIAMPolicyResult => getIAMPolicyResult.PolicyData),
    });

});

package generated_program;

import com.pulumi.Context;
import com.pulumi.Pulumi;
import com.pulumi.core.Output;
import com.pulumi.gcp.organizations.OrganizationsFunctions;
import com.pulumi.gcp.organizations.inputs.GetIAMPolicyArgs;
import com.pulumi.gcp.compute.BackendBucketIamPolicy;
import com.pulumi.gcp.compute.BackendBucketIamPolicyArgs;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;

public class App {
    public static void main(String[] args) {
        Pulumi.run(App::stack);
    }

    public static void stack(Context ctx) {
        final var admin = OrganizationsFunctions.getIAMPolicy(GetIAMPolicyArgs.builder()
            .bindings(GetIAMPolicyBindingArgs.builder()
                .role("roles/viewer")
                .members("user:jane@example.com")
                .build())
            .build());

        var policy = new BackendBucketIamPolicy("policy", BackendBucketIamPolicyArgs.builder()
            .project(imageBackend.project())
            .name(imageBackend.name())
            .policyData(admin.policyData())
            .build());

    }
}

resources:
  policy:
    type: gcp:compute:BackendBucketIamPolicy
    properties:
      project: ${imageBackend.project}
      name: ${imageBackend.name}
      policyData: ${admin.policyData}
variables:
  admin:
    fn::invoke:
      function: gcp:organizations:getIAMPolicy
      arguments:
        bindings:
          - role: roles/viewer
            members:
              - user:jane@example.com

The policyData property accepts output from getIAMPolicy, which defines bindings between roles and members. This resource is authoritative: it replaces any existing policy. You cannot use BackendBucketIamPolicy alongside BackendBucketIamBinding or BackendBucketIamMember, as they will conflict over policy ownership.

Grant a role to multiple members at once

When multiple users or service accounts need the same access level, BackendBucketIamBinding assigns them all to one role.

import * as pulumi from "@pulumi/pulumi";
import * as gcp from "@pulumi/gcp";

const binding = new gcp.compute.BackendBucketIamBinding("binding", {
    project: imageBackend.project,
    name: imageBackend.name,
    role: "roles/viewer",
    members: ["user:jane@example.com"],
});

import pulumi
import pulumi_gcp as gcp

binding = gcp.compute.BackendBucketIamBinding("binding",
    project=image_backend["project"],
    name=image_backend["name"],
    role="roles/viewer",
    members=["user:jane@example.com"])

package main

import (
	"github.com/pulumi/pulumi-gcp/sdk/v9/go/gcp/compute"
	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
)

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		_, err := compute.NewBackendBucketIamBinding(ctx, "binding", &compute.BackendBucketIamBindingArgs{
			Project: pulumi.Any(imageBackend.Project),
			Name:    pulumi.Any(imageBackend.Name),
			Role:    pulumi.String("roles/viewer"),
			Members: pulumi.StringArray{
				pulumi.String("user:jane@example.com"),
			},
		})
		if err != nil {
			return err
		}
		return nil
	})
}

using System.Collections.Generic;
using System.Linq;
using Pulumi;
using Gcp = Pulumi.Gcp;

return await Deployment.RunAsync(() => 
{
    var binding = new Gcp.Compute.BackendBucketIamBinding("binding", new()
    {
        Project = imageBackend.Project,
        Name = imageBackend.Name,
        Role = "roles/viewer",
        Members = new[]
        {
            "user:jane@example.com",
        },
    });

});

package generated_program;

import com.pulumi.Context;
import com.pulumi.Pulumi;
import com.pulumi.core.Output;
import com.pulumi.gcp.compute.BackendBucketIamBinding;
import com.pulumi.gcp.compute.BackendBucketIamBindingArgs;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;

public class App {
    public static void main(String[] args) {
        Pulumi.run(App::stack);
    }

    public static void stack(Context ctx) {
        var binding = new BackendBucketIamBinding("binding", BackendBucketIamBindingArgs.builder()
            .project(imageBackend.project())
            .name(imageBackend.name())
            .role("roles/viewer")
            .members("user:jane@example.com")
            .build());

    }
}

resources:
  binding:
    type: gcp:compute:BackendBucketIamBinding
    properties:
      project: ${imageBackend.project}
      name: ${imageBackend.name}
      role: roles/viewer
      members:
        - user:jane@example.com

The members property lists all identities that should have the specified role. This resource is authoritative for its role: it controls the complete member list for that role while preserving other roles in the policy. Only one BackendBucketIamBinding can exist per role.

Add a single member to a role incrementally

When you need to grant access to one user without affecting existing permissions, BackendBucketIamMember adds individual members.

import * as pulumi from "@pulumi/pulumi";
import * as gcp from "@pulumi/gcp";

const member = new gcp.compute.BackendBucketIamMember("member", {
    project: imageBackend.project,
    name: imageBackend.name,
    role: "roles/viewer",
    member: "user:jane@example.com",
});

import pulumi
import pulumi_gcp as gcp

member = gcp.compute.BackendBucketIamMember("member",
    project=image_backend["project"],
    name=image_backend["name"],
    role="roles/viewer",
    member="user:jane@example.com")

package main

import (
	"github.com/pulumi/pulumi-gcp/sdk/v9/go/gcp/compute"
	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
)

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		_, err := compute.NewBackendBucketIamMember(ctx, "member", &compute.BackendBucketIamMemberArgs{
			Project: pulumi.Any(imageBackend.Project),
			Name:    pulumi.Any(imageBackend.Name),
			Role:    pulumi.String("roles/viewer"),
			Member:  pulumi.String("user:jane@example.com"),
		})
		if err != nil {
			return err
		}
		return nil
	})
}

using System.Collections.Generic;
using System.Linq;
using Pulumi;
using Gcp = Pulumi.Gcp;

return await Deployment.RunAsync(() => 
{
    var member = new Gcp.Compute.BackendBucketIamMember("member", new()
    {
        Project = imageBackend.Project,
        Name = imageBackend.Name,
        Role = "roles/viewer",
        Member = "user:jane@example.com",
    });

});

package generated_program;

import com.pulumi.Context;
import com.pulumi.Pulumi;
import com.pulumi.core.Output;
import com.pulumi.gcp.compute.BackendBucketIamMember;
import com.pulumi.gcp.compute.BackendBucketIamMemberArgs;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;

public class App {
    public static void main(String[] args) {
        Pulumi.run(App::stack);
    }

    public static void stack(Context ctx) {
        var member = new BackendBucketIamMember("member", BackendBucketIamMemberArgs.builder()
            .project(imageBackend.project())
            .name(imageBackend.name())
            .role("roles/viewer")
            .member("user:jane@example.com")
            .build());

    }
}

resources:
  member:
    type: gcp:compute:BackendBucketIamMember
    properties:
      project: ${imageBackend.project}
      name: ${imageBackend.name}
      role: roles/viewer
      member: user:jane@example.com

The member property specifies a single identity to grant the role. This resource is non-authoritative: it adds one member while preserving all other members for the same role. You can use multiple BackendBucketIamMember resources for the same role, and they can coexist with BackendBucketIamBinding resources as long as they target different roles.

Beyond these examples

These snippets focus on specific IAM management features: authoritative vs non-authoritative IAM management and role-based access control. They’re intentionally minimal rather than full access control solutions.

The examples reference pre-existing infrastructure such as backend buckets (by name and project). They focus on configuring IAM permissions rather than provisioning the backend bucket itself.

To keep things focused, common IAM patterns are omitted, including:

Conditional IAM bindings (condition property)
Custom role definitions
Service account creation
Backend bucket provisioning

These omissions are intentional: the goal is to illustrate how each IAM resource type is wired, not provide drop-in access control modules. See the BackendBucketIamMember resource reference for all available configuration options.

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Frequently Asked Questions

Resource Selection & Conflicts

What's the difference between BackendBucketIamPolicy, BackendBucketIamBinding, and BackendBucketIamMember?

BackendBucketIamPolicy is fully authoritative and replaces the entire IAM policy. BackendBucketIamBinding is authoritative for a specific role, replacing all members for that role while preserving other roles. BackendBucketIamMember is non-authoritative, adding a single member to a role without affecting other members.

Can I use BackendBucketIamPolicy with BackendBucketIamBinding or BackendBucketIamMember?

No, BackendBucketIamPolicy cannot be used with BackendBucketIamBinding or BackendBucketIamMember because they will conflict over policy control. Choose either Policy alone (authoritative) or Binding/Member together (granular).

Can I use BackendBucketIamBinding and BackendBucketIamMember together?

Yes, but only if they manage different roles. Using both resource types for the same role will cause conflicts.

Configuration & Identity Formats

What member identity formats are supported?

Supported formats include:

allUsers or allAuthenticatedUsers for public/authenticated access
user:{email}, serviceAccount:{email}, group:{email} for specific identities
domain:{domain} for G Suite domains
projectOwner:{projectid}, projectEditor:{projectid}, projectViewer:{projectid} for project roles
Federated identities like principal://iam.googleapis.com/locations/global/workforcePools/...

How do I specify a custom IAM role?

Custom roles must use the format [projects|organizations]/{parent-name}/roles/{role-name}, for example projects/my-project/roles/my-custom-role.

Immutability & Limitations

What properties can't be changed after creating a BackendBucketIamMember?

All input properties are immutable: member, role, name, project, and condition. Changing any of these requires recreating the resource.

Is BackendBucketIamMember production-ready?

This resource is in beta and requires the terraform-provider-google-beta provider. Consider beta stability for production use.

Using a different cloud?

Explore security guides for other cloud providers:

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