If you are attempting to run “terraform init” with a Google Cloud Storage backend and get the following error:
Error: Failed to get existing workspaces: querying Cloud Storage failed: storage: bucket doesn't exist
The first check should be that the Google Cloud Storage bucket indeed exists, using gsutil.
project_id=myproject-123 gsutil ls -p $project_id
If the GCS bucket does exist and your terraform Google provider is relying on ‘gcloud auth application-default’ for credentials (versus an explicit account), then make sure the login context is set to the expected GCP project using the command below.
gcloud auth application-default login --project $project_id
Because the error message can be indicative of the login context (in well-known location) being set to an older or unexpected GCP project.
cat ~/.config/gcloud/application_default_credentials.json
REFERENCES
google, how ADC works and well-known locations
gcloud auth application-default
devcoops.com, ways to deal with ‘querying Cloud Storage failed’