These are commonly raised concerns, all of which have answers much simpler than "install this giant distributed system". I'll go ahead and answer them since I take the questions to be in good faith...
> How do you run an application on a cluster of plain old linux machines?
Build a package, install it in an image, run that image in an autoscaling group (or whatever equivalent your cloud of choice offers).
> How do you do load balancing?
An Elastic Load Balancer (v1 or v2), HAProxy, an F5 - this is deployment environment specific (just like in Kubernetes).
> How do you update your app without downtime?
Blue-green deployment, or phased rollout.
> How do you ensure all your servers are running the same version of dependencies?
Build them from a common image.
> How do you update those dependencies?
Update the Packer template that builds that image.
> How do you replicate your environment if you want to add a new server to your cluster?
Start the server from the same image.
> If your app has microservices how do services discover each other?
Consul, or DNS, depending on your appetite.
> How do you mount volumes from cloud storage?
It's a bit unclear exactly what you mean here, but I'll assume you mean either block devices (just attach them at machine boot, or on startup if they need a claim), or NFS.
> How do you update configuration?
Either update Consul and have it propagate configuration, or update a configuration package and push it out.
> How do you automatically restart failed applications?
Systemd restart policy.
> How do you monitor if your applications are working?
From outside - something like pingdom, and some kind of continuous testing. It's critical that this is measured from the perspective of a user.
> How do you make sure the right number of MongoDB replicas are running at all times?
Somewhat flippant answer here: the right number of MongoDB servers is zero. More generally, by limiting the size of an autoscaling group.
> How do you view your log files remotely?
Cloudwatch, Syslog, SSH (depending on requirements).
> How do you port-forward from localhost to your Linux server to test your app locally?
SSH.