GCE + Load Balancer + Instance without public IP - google-compute-engine

Question

I have instance that on purpose does not have public IP.
I have GCE Network Load Balancer that is using above instance as target pool.
Everything works great.
Then I wanted my instance to communicate with internet so I followed this documentation: https://cloud.google.com/compute/docs/networking#natgateway (Configuring a NAT gateway)
Instance can communicate with internet fine but load balancer cannot communicate with my instance anymore.
I think that these steps create the issue with loadbalancer:
$ gcloud compute routes create no-ip-internet-route --network gce-network \
--destination-range 0.0.0.0/0 \
--next-hop-instance nat-gateway \
--next-hop-instance-zone us-central1-a \
--tags no-ip --priority 800
user#nat-gateway:~$ sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
```
Do you know what can be done to make both things work together ?

Answer 1

I have recreated the environment you've described and did not run into any issues.
$ gcloud compute routes create no-ip-internet-route --network gce-network \
--destination-range 0.0.0.0/0 \
--next-hop-instance nat-gateway \
--next-hop-instance-zone us-central1-a \
--tags no-ip --priority 800
The only thing that the above command will do, is create a routing rule so that instances with no external traffic are pointed to the NAT gateway for any traffic they want need to send out. This will not affect the LB's ability to reach your instance.
In my test, I followed the exact guide you referenced, which you can find here, and that results in:
1 new network
1 firewall rule to allow SSH on port 22
1 firewall rule to allow all internal traffic
1 new instance to act as a NAT Gateway
1 new instance internal instance with no external IP address
I also added the internal instance to a 'TargetPool' and created an LB for the purpose of the test.
My internal instance was accessible both via the LB's external address and internally via the NAT Gateway. The internal instance was also able to communicate with the Internet due to the NAT Gateway's configuration. Everything works as expected.
My recommendation for you and other readers (as this post is now rather old) is to try again. Make sure that you do not have any other conflicting rules, routes or software.