Manage GCP Spanner Instance IAM Permissions

The gcp:spanner/instanceIAMBinding:InstanceIAMBinding resource, part of the Pulumi GCP provider, manages IAM role bindings for Spanner instances by granting a specific role to a list of members. This guide focuses on two capabilities: authoritative role binding that replaces all members for a role, and non-authoritative member addition using InstanceIAMMember.

IAM resources reference existing Spanner instances. InstanceIAMBinding is authoritative for a given role, meaning it replaces all members for that role while preserving other roles. It can be used alongside InstanceIAMMember resources as long as they don’t grant the same role. The examples are intentionally small. Combine them with your own instance references and identity management.

Grant a role to multiple members

Teams managing Spanner access often need to grant the same role to multiple users or service accounts at once.

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

const instance = new gcp.spanner.InstanceIAMBinding("instance", {
    instance: "your-instance-name",
    role: "roles/spanner.databaseAdmin",
    members: ["user:jane@example.com"],
});

import pulumi
import pulumi_gcp as gcp

instance = gcp.spanner.InstanceIAMBinding("instance",
    instance="your-instance-name",
    role="roles/spanner.databaseAdmin",
    members=["user:jane@example.com"])

package main

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

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		_, err := spanner.NewInstanceIAMBinding(ctx, "instance", &spanner.InstanceIAMBindingArgs{
			Instance: pulumi.String("your-instance-name"),
			Role:     pulumi.String("roles/spanner.databaseAdmin"),
			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 instance = new Gcp.Spanner.InstanceIAMBinding("instance", new()
    {
        Instance = "your-instance-name",
        Role = "roles/spanner.databaseAdmin",
        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.spanner.InstanceIAMBinding;
import com.pulumi.gcp.spanner.InstanceIAMBindingArgs;
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 instance = new InstanceIAMBinding("instance", InstanceIAMBindingArgs.builder()
            .instance("your-instance-name")
            .role("roles/spanner.databaseAdmin")
            .members("user:jane@example.com")
            .build());

    }
}

resources:
  instance:
    type: gcp:spanner:InstanceIAMBinding
    properties:
      instance: your-instance-name
      role: roles/spanner.databaseAdmin
      members:
        - user:jane@example.com

The members property lists all identities that should have the specified role. When you apply this configuration, it replaces any existing members for roles/spanner.databaseAdmin while leaving other roles untouched. The instance property identifies which Spanner instance to configure.

Add a single member to a role

When onboarding individual users or granting access to specific service accounts, you can add one member without affecting existing members.

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

const instance = new gcp.spanner.InstanceIAMMember("instance", {
    instance: "your-instance-name",
    role: "roles/spanner.databaseAdmin",
    member: "user:jane@example.com",
});

import pulumi
import pulumi_gcp as gcp

instance = gcp.spanner.InstanceIAMMember("instance",
    instance="your-instance-name",
    role="roles/spanner.databaseAdmin",
    member="user:jane@example.com")

package main

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

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		_, err := spanner.NewInstanceIAMMember(ctx, "instance", &spanner.InstanceIAMMemberArgs{
			Instance: pulumi.String("your-instance-name"),
			Role:     pulumi.String("roles/spanner.databaseAdmin"),
			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 instance = new Gcp.Spanner.InstanceIAMMember("instance", new()
    {
        Instance = "your-instance-name",
        Role = "roles/spanner.databaseAdmin",
        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.spanner.InstanceIAMMember;
import com.pulumi.gcp.spanner.InstanceIAMMemberArgs;
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 instance = new InstanceIAMMember("instance", InstanceIAMMemberArgs.builder()
            .instance("your-instance-name")
            .role("roles/spanner.databaseAdmin")
            .member("user:jane@example.com")
            .build());

    }
}

resources:
  instance:
    type: gcp:spanner:InstanceIAMMember
    properties:
      instance: your-instance-name
      role: roles/spanner.databaseAdmin
      member: user:jane@example.com

The InstanceIAMMember resource adds a single member to a role non-authoritatively. Unlike InstanceIAMBinding, it doesn’t replace existing members. The member property uses the same identity format as members in InstanceIAMBinding (user:, serviceAccount:, group:, domain:, or special identifiers like allUsers).

Beyond these examples

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

The examples reference pre-existing infrastructure such as Spanner instances. They focus on configuring IAM bindings rather than provisioning instances or defining custom roles.

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

Conditional IAM bindings (condition property)
Project-level configuration (project property)
Policy-level management (InstanceIAMPolicy)
Custom role definitions

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

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Frequently Asked Questions

Resource Selection & Conflicts

What's the difference between InstanceIAMPolicy, InstanceIAMBinding, and InstanceIAMMember?

gcp.spanner.InstanceIAMPolicy is authoritative and replaces the entire IAM policy. gcp.spanner.InstanceIAMBinding is authoritative for a specific role but preserves other roles. gcp.spanner.InstanceIAMMember is non-authoritative and preserves other members for the same role.

Can I lock myself out of my Spanner instance with InstanceIAMPolicy?

Yes, using gcp.spanner.InstanceIAMPolicy replaces the entire IAM policy and removes any default permissions not explicitly included in your configuration. Include all necessary permissions or use gcp.spanner.InstanceIAMBinding or gcp.spanner.InstanceIAMMember for safer incremental updates.

Which IAM resources can I use together?

gcp.spanner.InstanceIAMPolicy cannot be used with gcp.spanner.InstanceIAMBinding or gcp.spanner.InstanceIAMMember (they’ll conflict). However, gcp.spanner.InstanceIAMBinding and gcp.spanner.InstanceIAMMember can be used together only if they don’t grant privileges to the same role.

When should I use InstanceIAMBinding vs InstanceIAMMember?

Use gcp.spanner.InstanceIAMBinding when you want to manage all members for a specific role (authoritative for that role). Use gcp.spanner.InstanceIAMMember when you want to add individual members without affecting other members for the same role (non-authoritative).

Configuration & Immutability

What properties can't be changed after creation?

The instance, role, project, and condition properties are all immutable and require resource replacement if changed.

What format do custom roles need to follow?

Custom roles must use the format [projects|organizations]/{parent-name}/roles/{role-name}.

Member Identity Formats

How do I specify different types of members?

Use these format prefixes in the members array:

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)
principal:{principal} - Federated single identity
principalSet:{principalSet} - Federated identity group

Using a different cloud?

Explore iam guides for other cloud providers:

AWS Guides Azure Guides