[SOLVED] Error: multiple EC2 Instances matched; use additional constraints to reduce matches to a single EC2 Instance

When you are using data sources for aws_instance probably to fetch the IP address or something else,

data "aws_instance" "foo" {
  filter {
    name   = "tag:Name"
    values = ["instance-name"]
  }
}

You must have faced the following issues while using Terraform for EC2 instances.

│ Error: multiple EC2 Instances matched; use additional constraints to reduce matches to a single EC2 Instance

Why this issue occurs?

There’s a fair chance that the previous instance with the same name is destroyed, but there’s still an entry with the terminated state.

Resolution

In this case, you will need to add another filter that will only retrieve running instances, not the terminated ones.

data "aws_instance" "foo" {
  filter {
    name   = "tag:Name"
    values = ["instance-name"]
  }
  filter {
    name   = "instance-state-name"
    values = ["running"]
  } 
}

Note: instance_state field won’t work in this case.

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