AWS Parallel Cluster, head using image (AMI) that is used by 2 instances

Question

Setup:

I created an ec2 instance, took an image out of it and used it to create a second instance. I then created a cluster using pcluster and assigned the head node to this image.

Question

Once the cluster is deployed which ec2 instance will be used as head? If I specify the InstanceType will it automatically filter out the instances that have a different type?

Secondly, using this setup I am trying to submit a job. I can do it on the second instance, which is the one being used as the head, as shown when I run

pcluster describe-cluster -n clusterName

However it does not work when I try to submit it through the first instance. I get the error:

sinfo
sinfo: error: resolve_ctls_from_dns_srv: res_nsearch error: Unknown host
sinfo: error: fetch_config: DNS SRV lookup failed
sinfo: error: _establish_config_source: failed to fetch config
sinfo: fatal: Could not establish a configuration source

Considering both of them have the same image shouldn't they both be able to submit jobs?