How to fix Error: Error creating Pub/Sub Topic: AlreadyExists in Terraform

Check if the Pub/Sub topic actually exists in your GCP project using the gcloud CLI:

gcloud pubsub topics list --project=YOUR_PROJECT_ID

Or check the GCP Console under Pub/Sub > Topics. If you see the topic listed, it exists in Google Cloud but Terraform doesn't know about it.

Use terraform import to register the existing topic with Terraform so it can manage it going forward:

terraform import google_pubsub_topic.my_topic projects/YOUR_PROJECT_ID/topics/YOUR_TOPIC_NAME

Replace:
- my_topic: Your Terraform resource identifier (the name after google_pubsub_topic.)
- YOUR_PROJECT_ID: Your GCP project ID
- YOUR_TOPIC_NAME: The actual Pub/Sub topic name

Example:

terraform import google_pubsub_topic.events projects/my-gcp-project/topics/order-events

After successful import, Terraform will add the topic to your state file and stop trying to create it.

Make sure your HCL configuration matches the actual topic settings. Import brings in the resource, but you need to ensure your .tf file reflects reality:

resource "google_pubsub_topic" "my_topic" {
  name = "YOUR_TOPIC_NAME"
  project = "YOUR_PROJECT_ID"

  # Add any other existing settings here
  message_retention_duration = "86400s"  # If applicable
  labels = {
    environment = "production"
  }
}

Run terraform plan to verify there are no drift differences between your config and the actual topic.

If you're using the terraform-google-modules/pubsub module, you can reference an existing topic without recreating it:

module "pubsub" {
  source      = "terraform-google-modules/pubsub/google"
  version     = "~> 8.3"

  topic       = "existing-topic-name"
  project_id  = "my-project"
  create_topic = false  # Don't create, just reference existing
}

This allows the module to work with a pre-existing topic instead of trying to create one.

If the existing topic is not important or is in a development environment, you can delete it and let Terraform manage it cleanly:

# Using gcloud CLI
gcloud pubsub topics delete YOUR_TOPIC_NAME --project=YOUR_PROJECT_ID

# Or delete via GCP Console under Pub/Sub > Topics

Then run:

terraform apply

Terraform will create a fresh topic that it fully manages. Only use this approach in development/test environments, not production.

To avoid conflicts in team environments:

1. Use a remote backend with state locking (Cloud Storage, Terraform Cloud):

terraform {
  backend "gcs" {
    bucket = "my-terraform-state"
    prefix = "pubsub"
  }
}

2. Always run `terraform plan` before apply to catch conflicts early:

terraform plan -out=tfplan
terraform apply tfplan

3. Communicate with your team before creating resources manually—keep all infrastructure in Terraform.

4. Use `for_each` or `count` carefully to avoid duplicate resource names in your configuration.