gcloud app instances enable-debug

NAME: gcloud app instances enable-debug - enable debug mode for an instance (only works on the flexible environment)
SYNOPSIS: gcloud app instances enable-debug [INSTANCE] [--service=SERVICE, -s SERVICE] [--version=VERSION, -v VERSION] [GCLOUD_WIDE_FLAG …]
DESCRIPTION: When in debug mode, SSH will be enabled on the VMs, and you can use gcloud compute ssh to login to them. They will be removed from the health checking pools, but they still receive requests.
Note that any local changes to an instance will be lost if debug mode is disabled on the instance. New instance(s) may spawn depending on the app's scaling settings.
Additionally, debug mode doesn't work for applications using the App Engine standard environment.
EXAMPLES: To enable debug mode for a particular instance, run:
gcloud app instances enable-debug --service=s1 --version=v1 i1

To enable debug mode for an instance chosen interactively, run:
gcloud app instances enable-debug
POSITIONAL ARGUMENTS: [INSTANCE]

Instance ID to enable debug mode on. If not specified, select instance interactively. Must uniquely specify (with other flags) exactly one instance
FLAGS: --service=SERVICE, -s SERVICE

If specified, only match instances belonging to the given service. This affects both interactive and non-interactive selection.

--version=VERSION, -v VERSION

If specified, only match instances belonging to the given version. This affects both interactive and non-interactive selection.
GCLOUD WIDE FLAGS: These flags are available to all commands: --access-token-file, --account, --billing-project, --configuration, --flags-file, --flatten, --format, --help, --impersonate-service-account, --log-http, --project, --quiet, --trace-token, --user-output-enabled, --verbosity.
Run $ gcloud help for details.
NOTES: This variant is also available:
gcloud beta app instances enable-debug