Manage GCP Pub/Sub Topic IAM Permissions

The gcp:pubsub/topicIAMMember:TopicIAMMember resource, part of the Pulumi GCP provider, manages IAM permissions for Pub/Sub topics by adding individual members to roles without affecting other members. This guide focuses on three approaches: non-authoritative single-member grants, authoritative role-level member lists, and complete policy replacement.

GCP provides three related resources for topic IAM management. TopicIAMMember adds one identity to a role (non-authoritative). TopicIAMBinding defines all members for a role (authoritative for that role). TopicIAMPolicy replaces the entire policy (fully authoritative). TopicIAMPolicy cannot be combined with the other two resources; TopicIAMBinding and TopicIAMMember can coexist only if they manage different roles. The examples are intentionally small. Combine them with your own topic references and identity management.

Grant a role to a single member

Most IAM configurations start by granting a specific role to one identity, preserving other members who already have the same role.

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

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

import pulumi
import pulumi_gcp as gcp

member = gcp.pubsub.TopicIAMMember("member",
    project=example["project"],
    topic=example["name"],
    role="roles/viewer",
    member="user:jane@example.com")

package main

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

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		_, err := pubsub.NewTopicIAMMember(ctx, "member", &pubsub.TopicIAMMemberArgs{
			Project: pulumi.Any(example.Project),
			Topic:   pulumi.Any(example.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.PubSub.TopicIAMMember("member", new()
    {
        Project = example.Project,
        Topic = example.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.pubsub.TopicIAMMember;
import com.pulumi.gcp.pubsub.TopicIAMMemberArgs;
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 TopicIAMMember("member", TopicIAMMemberArgs.builder()
            .project(example.project())
            .topic(example.name())
            .role("roles/viewer")
            .member("user:jane@example.com")
            .build());

    }
}

resources:
  member:
    type: gcp:pubsub:TopicIAMMember
    properties:
      project: ${example.project}
      topic: ${example.name}
      role: roles/viewer
      member: user:jane@example.com

The member property specifies one identity using formats like “user:jane@example.com” or “serviceAccount:app@project.iam.gserviceaccount.com”. The role property defines the permission level. This non-authoritative approach adds the member without removing others who have the same role on the topic.

Grant a role to multiple members authoritatively

When you need to define the complete list of identities for a role, TopicIAMBinding replaces all existing members for that role.

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

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

import pulumi
import pulumi_gcp as gcp

binding = gcp.pubsub.TopicIAMBinding("binding",
    project=example["project"],
    topic=example["name"],
    role="roles/viewer",
    members=["user:jane@example.com"])

package main

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

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		_, err := pubsub.NewTopicIAMBinding(ctx, "binding", &pubsub.TopicIAMBindingArgs{
			Project: pulumi.Any(example.Project),
			Topic:   pulumi.Any(example.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.PubSub.TopicIAMBinding("binding", new()
    {
        Project = example.Project,
        Topic = example.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.pubsub.TopicIAMBinding;
import com.pulumi.gcp.pubsub.TopicIAMBindingArgs;
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 TopicIAMBinding("binding", TopicIAMBindingArgs.builder()
            .project(example.project())
            .topic(example.name())
            .role("roles/viewer")
            .members("user:jane@example.com")
            .build());

    }
}

resources:
  binding:
    type: gcp:pubsub:TopicIAMBinding
    properties:
      project: ${example.project}
      topic: ${example.name}
      role: roles/viewer
      members:
        - user:jane@example.com

The members property takes an array of identity strings. This resource is authoritative for the specified role: it replaces any existing members for “roles/viewer” but preserves other roles on the topic. Use this when you want to control exactly who has a specific role.

Replace the entire IAM policy for a topic

Organizations managing IAM centrally often set the complete policy document, replacing any existing bindings.

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.pubsub.TopicIAMPolicy("policy", {
    project: example.project,
    topic: example.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.pubsub.TopicIAMPolicy("policy",
    project=example["project"],
    topic=example["name"],
    policy_data=admin.policy_data)

package main

import (
	"github.com/pulumi/pulumi-gcp/sdk/v9/go/gcp/organizations"
	"github.com/pulumi/pulumi-gcp/sdk/v9/go/gcp/pubsub"
	"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 = pubsub.NewTopicIAMPolicy(ctx, "policy", &pubsub.TopicIAMPolicyArgs{
			Project:    pulumi.Any(example.Project),
			Topic:      pulumi.Any(example.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.PubSub.TopicIAMPolicy("policy", new()
    {
        Project = example.Project,
        Topic = example.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.pubsub.TopicIAMPolicy;
import com.pulumi.gcp.pubsub.TopicIAMPolicyArgs;
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 TopicIAMPolicy("policy", TopicIAMPolicyArgs.builder()
            .project(example.project())
            .topic(example.name())
            .policyData(admin.policyData())
            .build());

    }
}

resources:
  policy:
    type: gcp:pubsub:TopicIAMPolicy
    properties:
      project: ${example.project}
      topic: ${example.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 a complete IAM policy document, typically retrieved from getIAMPolicy. This resource is fully authoritative: it replaces the topic’s entire IAM policy with the provided document. TopicIAMPolicy cannot be used alongside TopicIAMBinding or TopicIAMMember because they would conflict over policy ownership.

Beyond these examples

These snippets focus on specific IAM management approaches: single-member grants, role-level member lists, and complete policy replacement. They’re intentionally minimal rather than full access control configurations.

The examples reference pre-existing infrastructure such as Pub/Sub topics and a GCP project with appropriate permissions. They focus on configuring IAM bindings rather than provisioning topics or managing identities.

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

Conditional IAM bindings (condition property)
Custom role definitions
Federated identity configuration
Service account creation and management

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 TopicIAMMember resource reference for all available configuration options.

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Frequently Asked Questions

Resource Selection & Conflicts

Why am I getting IAM policy conflicts between my Pub/Sub topic resources?

TopicIAMPolicy cannot be used with TopicIAMBinding or TopicIAMMember because they will conflict over policy state. Use TopicIAMPolicy alone, or use TopicIAMBinding and TopicIAMMember without TopicIAMPolicy.

Which IAM resource should I use for my Pub/Sub topic?

Choose based on your needs:

TopicIAMPolicy: Authoritative, replaces the entire IAM policy
TopicIAMBinding: Authoritative for a specific role, preserves other roles
TopicIAMMember: Non-authoritative, adds a single member while preserving other members for the role

Can I use TopicIAMBinding and TopicIAMMember together?

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

Identity & Role Configuration

What member identity formats are supported?

Supported formats include:

allUsers: Anyone on the internet
allAuthenticatedUsers: Anyone with a Google account
user:{email}: Specific Google account (e.g., user:alice@gmail.com)
serviceAccount:{email}: Service account (e.g., serviceAccount:my-app@appspot.gserviceaccount.com)
group:{email}: Google group (e.g., group:admins@example.com)
domain:{domain}: G Suite domain (e.g., domain:example.com)
projectOwner:projectid, projectEditor:projectid, projectViewer:projectid: Project-level identities
Federated identities: Workload/workforce identity pools (e.g., principal://iam.googleapis.com/...)

How do I specify custom roles?

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

Resource Behavior

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

All input properties are immutable: member, role, topic, project, and condition. You must recreate the resource to change any of these.

Do I need to specify the project for TopicIAMMember?

Not necessarily. If not provided, the project will be inferred from the parent topic resource or the provider configuration.

Using a different cloud?

Explore security guides for other cloud providers:

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