Host key verification failed in google compute engine based mpich cluster - google-cloud-platform

Question

TLDR:
I have 2 google compute engine instances, I've installed mpich on both.
When I try to run a sample I get Host key verification failed.
Detailed version:
I've followed this tutorial in order to get this task done: http://mpitutorial.com/tutorials/running-an-mpi-cluster-within-a-lan/.
I have 2 google compute engine vms with ubuntu 14.04 (the google cloud account is a trial one, btw). I've downloaded this version of mpich on both instances: http://www.mpich.org/static/downloads/3.3rc1
/mpich-3.3rc1.tar.gz and I installed it using these steps:
./configure --disable-fortran
sudo make
sudo make install
This is the way the /etc/hosts file looks on the master-node:
127.0.0.1 localhost
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
169.254.169.254 metadata.google.internal metadata
10.128.0.3 client
10.128.0.2 master
10.128.0.2 linux1.us-central1-c.c.ultimate-triode-161918.internal linux
1 # Added by Google
169.254.169.254 metadata.google.internal # Added by Google
And this is the way the /etc/hosts file looks on the client-node:
127.0.0.1 localhost
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
169.254.169.254 metadata.google.internal metadata
10.128.0.2 master
10.128.0.3 client
10.128.0.3 linux2.us-central1-c.c.ultimate-triode-161918.internal linux
2 # Added by Google
169.254.169.254 metadata.google.internal # Added by Google
The rest of the steps involved adding an user named mpiuser on both nodes and configuring passwordless ssh authentication between the nodes. And configuring a cloud shared directory between nodes.
The configuration worked till this point. I've downloaded this file https://raw.githubusercontent.com/pmodels/mpich/master/examples/cpi.c to /home/mpiuser/cloud/mpi_sample.c, compiled it this way:
mpicc -o mpi_sample mpi_sample.c
and issued this command on the master node while logged in as the mpiuser:
mpirun -np 2 -hosts client,master ./mpi_sample
and I got this error:
Host key verification failed.
What's wrong? I've tried to troubleshoot this problem over more than 2 days but I can't get a valid solution.

Answer 1

Add
package-lock.json
in ".gcloudignore file".
And deploy it again.

Answer 2

It turned out that my password less ssh wasn't configured properly. I've created 2 new instances and did the following things to get a working password less and thus get a working version of that sample. The following steps were execute on an ubuntu server 18.04.
First, by default, instances on google cloud have PasswordAuthentication setting turned off. In the client server do:
sudo vim /etc/ssh/sshd_config
and change PasswordAuthentication no to PasswordAuthentication yes. Then
sudo systemctl restart ssh
Generate a ssh key from the master server with:
ssh-keygen -t rsa -b 4096 -C "user.mail#server.com"
Copy the generated ssh key from the master server to the client
ssh-copy-id client
Now you get a fully functional password less ssh from master to client. However mpich still failed.
The additional steps that I did was to copy the public key to the ~/.ssh/authorized_keys file, both on master and client. So execute this command from both servers:
sudo cat .ssh/id_rsa.pub >> .ssh/authorized_keys
Then make sure the /etc/ssh/sshd_config files from both the client and server have the following configurations:
PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM no
Restart the ssh service from both client and master
sudo systemctl restart ssh
And that's it, mpich works smoothly now.