Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/terraform/exercises/s3_bucket_rename/exercise.md

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+# Rename S3 Bucket
+
+## Requirements
+
+* An existing S3 bucket tracked by Terraform.
+If you don't have it, you can use the following block and run `terraform apply`:
+
+```terraform
+resource "aws_s3_bucket" "some_bucket" {
+    bucket = "some-old-bucket"
+}
+```
+
+## Objectives
+
+1. Rename an existing S3 bucket and make sure it's still tracked by Terraform
+
+## Solution
+
+Click [here to view the solution](solution.md)

topics/terraform/exercises/s3_bucket_rename/solution.md

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+# Rename S3 Bucket
+
+## Requirements
+
+* An existing S3 bucket tracked by Terraform.
+If you don't have it, you can use the following block and run `terraform apply`:
+
+```terraform
+resource "aws_s3_bucket" "some_bucket" {
+    bucket = "some-old-bucket"
+}
+```
+
+## Objectives
+
+1. Rename an existing S3 bucket and make sure it's still tracked by Terraform
+
+## Solution
+
+```sh
+# A bucket name is immutable in AWS so we'll have to create a new bucket
+aws s3 mb s3://some-new-bucket-123
+
+# Sync old bucket to new bucket
+aws s3 sync s3://some-old-bucket s3://some-new-bucket-123
+
+# Remove the old bucket from Terraform's state
+terraform state rm aws_s3_bucket.some_bucket
+
+# Import new bucket to Terraform's state
+terraform import aws_s3_bucket.some_bucket some-new-bucket-123
+
+: '
+aws_s3_bucket.some_bucket: Refreshing state... [id=some-new-bucket-123]
+
+Import successful!
+The resources that were imported are shown above. These resources are now in
+your Terraform state and will henceforth be managed by Terraform.
+'
+
+# Modify the Terraform definition to include the new name
+# resource "aws_s3_bucket" "some_bucket" {
+#    bucket = "some-new-bucket-123"
+# }
+
+# Remove old bucket
+aws s3 rm s3://some-old-bucket --recursive
+aws s3 rb s3://some-old-bucket
+```