Service start request repeated too quickly, refusing to start

2610 ExecStart=/opt/bitnami/nodejs/bin/node /home/user/c9sdk/server.js -w /home/user -l 0.0.0.0 -a admin:admin (code=exited, status=216/GROUP)
…
Oct 13 07:21:02 test-vm systemd[1]: cloud9.service: main process exited, code=exited, status=216/GROUP

… which describes the problem. Your group nobody is not a valid group on your system. Specify a valid group.

Environment=PATH=/bin:/usr/bin:/usr/local/bin

This is probably unnecessary.

-w /home/user -l 0.0.0.0

In a better world, the cloud9 service program here would receive its listening socket as an open file descriptor, and inherit its working directory (which, ironically, you have explicitly set elsewhere in the unit).

Further reading

  • https://unix.stackexchange.com/a/316168/5132

Removing the Restart parameter and adding a valid user/group helped me to solve the problem.

[Unit]
Description=cloud9

[Service]
ExecStart=/opt/bitnami/nodejs/bin/node /home/user/c9sdk/server.js -w /home/user -l 0.0.0.0 -a admin:admin
User=user
Group=group
Environment=PATH=/bin:/usr/bin:/usr/local/bin
Environment=NODE_ENV=production
WorkingDirectory=/home/user/c9sdk

[Install]
WantedBy=multi-user.target