Repository: go
Issue: x/build/cmd/gomote: SSH to AWS ARM gomotes sometimes fails
Labels: Builders,NeedsInvestigation

It seems like some gomotes are permanently broken, but new ones are OK?

```
$ gomote ssh user-mpratt-linux-arm64-aws-0
$ ssh -p 2222 user-mpratt-linux-arm64-aws-0@farmer.golang.org # auth using https://github.com/prattmic.keys
# Welcome to the gomote ssh proxy, mpratt.
# Connecting to/starting remote ssh...
#
failed to connect to ssh on user-mpratt-linux-arm64-aws-0: unexpected /connect-ssh response: 502 Bad Gateway, dial tcp 127.0.0.1:22: connect: connection refused

Connection to farmer.golang.org closed.
$ gomote ssh user-mpratt-linux-arm64-aws-0
$ ssh -p 2222 user-mpratt-linux-arm64-aws-0@farmer.golang.org # auth using https://github.com/prattmic.keys
# Welcome to the gomote ssh proxy, mpratt.
# Connecting to/starting remote ssh...
#
failed to connect to ssh on user-mpratt-linux-arm64-aws-0: unexpected /connect-ssh response: 502 Bad Gateway, dial tcp 127.0.0.1:22: connect: connection refused

Connection to farmer.golang.org closed.
$ gomote create linux-arm64-aws           
# still creating linux-arm64-aws after 5s; 0 requests ahead of you
# still creating linux-arm64-aws after 10s; 0 requests ahead of you
# still creating linux-arm64-aws after 15s; 0 requests ahead of you
# still creating linux-arm64-aws after 20s; 0 requests ahead of you
# still creating linux-arm64-aws after 25s; 0 requests ahead of you
# still creating linux-arm64-aws after 30s; 0 requests ahead of you
# still creating linux-arm64-aws after 35s; 0 requests ahead of you
user-mpratt-linux-arm64-aws-1
$ gomote ssh user-mpratt-linux-arm64-aws-1
$ ssh -p 2222 user-mpratt-linux-arm64-aws-1@farmer.golang.org # auth using https://github.com/prattmic.keys
# Welcome to the gomote ssh proxy, mpratt.
# Connecting to/starting remote ssh...
#
# `gomote push` and the builders use:
# - workdir: /workdir
# - GOROOT: /workdir/go
# - GOPATH: /workdir/gopath
# - env: GO_BUILDER_NAME=linux-arm64-aws GOROOT_BOOTSTRAP=/usr/local/go-bootstrap
# Happy debugging.
Warning: Permanently added '[localhost]:38283' (ECDSA) to the list of known hosts.
Linux 68c8a20ccbb8 4.19.0-12-arm64 #1 SMP Debian 4.19.152-1 (2020-10-18) aarch64

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.
debug1: PAM: reinitializing credentials
debug1: permanently_set_uid: 0/0
Environment:
  USER=root
  LOGNAME=root
  HOME=/root
  PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
  MAIL=/var/mail/root
  SHELL=/bin/bash
  TERM=screen
  SSH_CLIENT=127.0.0.1 45848 22
  SSH_CONNECTION=127.0.0.1 45848 127.0.0.1 22
  SSH_TTY=/dev/pts/0
root@68c8a20ccbb8:~#
```

i.e., the old instance doesn't seem to work at all. The new instance works fine. I've had this SSH issue on two different instances today (`linux-arm-aws` and `linux-arm64-aws`). FWIW, the broken ones I did various `gomote run` commands on (successfully) before attempting to SSH, while the working ones I SSH'd immediately.

cc @golang/release