The problem:I have Amazon EC2 running an application. It functions without issue when there is only one instance and no load balancer.But in my production environment, I have two identical instances running behind one load-balancer and when performing certain tasks, like a feature that generates a PDF and attaches it to an email, nothing happens at all, and when using Google Developer tools with the Network tab I get the error "504 Gateway Timeout" once the timeout hits (I have it set at 30 seconds).My Database is external, on Amazon RDS.I think... If I could force a client to stay connected to the initial server they logged in at, this problem would be solved, because it's my understanding that the 504 Gateway Timeout is happening when instance-1 tries to reach out to instance-2 to perform the task.This happens ONLY WHEN using Load Balancing, but never when connecting straight to one of my two servers.Load Balancer Settings:The load balancer has a CRECORD on my Registrar, so app.myapplication.com points to myloadbalancerDNSname.elb.amazonaws.com.The load balancer has 2 healthy instances, each in the same region but they are in different availability zones.The load balancer is using the same Security Groups as the Instances (allow ALL IPs on ports 22, 80, and 443).The load balancer has cross-zone load balancing turned on.CORS (in Amazon S3) is enabled to GET, POST, PUT, DELETE from * to * (I have no idea how this is associated with my instances but anyway I did it as the instructions said).The load balancer has listeners configured as such:Load Balancer Protocol:HTTP Load Balancer Port:80 Instance Protocol:HTTP Instance Port:80Load Balancer Protocol:HTTPS Load Balancer Port:443 Instance Protocol:HTTP Instance Port:80 (cipher chosen correctly per my Cert provider, and SSL fields 100% surely correct).Any help would be very much appreciated.

504 Gateway Timeout - Two EC2 instances with load balancer

The problem:

I have Amazon EC2 running an application. It functions without issue when there is only one instance and no load balancer.

But in my production environment, I have two identical instances running behind one load-balancer and when performing certain tasks, like a feature that generates a PDF and attaches it to an email, nothing happens at all, and when using Google Developer tools with the Network tab I get the error "504 Gateway Timeout" once the timeout hits (I have it set at 30 seconds).

My Database is external, on Amazon RDS.

I think... If I could force a client to stay connected to the initial server they logged in at, this problem would be solved, because it's my understanding that the 504 Gateway Timeout is happening when instance-1 tries to reach out to instance-2 to perform the task.

This happens ONLY WHEN using Load Balancing, but never when connecting straight to one of my two servers.

Load Balancer Settings:

The load balancer has a CRECORD on my Registrar, so app.myapplication.com points to myloadbalancerDNSname.elb.amazonaws.com.
The load balancer has 2 healthy instances, each in the same region but they are in different availability zones.
The load balancer is using the same Security Groups as the Instances (allow ALL IPs on ports 22, 80, and 443).
The load balancer has cross-zone load balancing turned on.
CORS (in Amazon S3) is enabled to GET, POST, PUT, DELETE from * to * (I have no idea how this is associated with my instances but anyway I did it as the instructions said).
The load balancer has listeners configured as such:
Load Balancer Protocol:HTTP Load Balancer Port:80 Instance Protocol:HTTP Instance Port:80
Load Balancer Protocol:HTTPS Load Balancer Port:443 Instance Protocol:HTTP Instance Port:80 (cipher chosen correctly per my Cert provider, and SSL fields 100% surely correct).

Any help would be very much appreciated.