❯ gcloud compute ssh test-instance  --project test-project --zone asia-northeast1-a
WARNING: The public SSH key file for gcloud does not exist.
WARNING: The private SSH key file for gcloud does not exist.
WARNING: You do not have an SSH key for gcloud.
WARNING: SSH keygen will be executed to generate a key.
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /Users/hoge/.ssh/google_compute_engine.
Your public key has been saved in /Users/hoge/.ssh/google_compute_engine.pub.
The key fingerprint is:
SHA256:PQXtls0bpoISsn+/u2vDpqMKBORO5VEFgEGqyJ4klcM hoge@MAC00011
The key's randomart image is:
+---[RSA 2048]----+
|.+o+ooo.  ..     |
|+oo..      ..    |
|ooE.       ..+   |
|*o .. .  . .+ =  |
|++.  o .S.o. o o |
|+.. . . . ... .  |
| o.  . . . .     |
|   .  . o =      |
|    ...o.***     |
+----[SHA256]-----+
Updating project ssh metadata...⠹Updated [https://www.googleapis.com/compute/v1/projects/test-project].
Updating project ssh metadata...done.
Waiting for SSH key to propagate.
Warning: Permanently added 'compute.3504985360589690116' (ECDSA) to the list of known hosts.
Linux test-instance 4.9.0-12-amd64 #1 SMP Debian 4.9.210-1 (2020-01-20) x86_64

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
hoge@test-instance:~$

❯ ls ~/.ssh
config                     google_compute_engine      google_compute_engine.pub  google_compute_known_hosts

❯ gcloud compute config-ssh --project test-project
You should now be able to use ssh/scp with your instances.
For example, try running:

  $ ssh test-instance.asia-northeast1-a.test-project

❯ cat ~/.ssh/config

...

# Google Compute Engine Section
#
# The following has been auto-generated by "gcloud compute config-ssh"
# to make accessing your Google Compute Engine virtual machines easier.
#
# To remove this blob, run:
#
#   gcloud compute config-ssh --remove
#
# You can also manually remove this blob by deleting everything from
# here until the comment that contains the string "End of Google Compute
# Engine Section".
#
# You should not hand-edit this section, unless you are deleting it.
#
Host test-instance.asia-northeast1-a.test-project
    HostName 35.200.9.109
    IdentityFile /Users/hoge/.ssh/google_compute_engine
    UserKnownHostsFile=/Users/hoge/.ssh/google_compute_known_hosts
    HostKeyAlias=compute.3504985360589690116
    IdentitiesOnly=yes
    CheckHostIP=no

# End of Google Compute Engine Section

❯ ssh test-instance.asia-northeast1-a.test-project
Last login: Sun Feb 16 11:58:05 2020 from 126.228.201.100
hoge@test-instance:~$