<p>Can we run an application that is configured to run on multi-node AWS EC2 K8s cluster using kops (<a href="https://github.com/hydro-project/cluster/blob/master/docs/getting-started-aws.md" rel="nofollow noreferrer">project link</a>) into local Kubernetes cluster (setup using kubeadm)?</p>
<p>My thinking is that if the application runs in k8s cluster based on AWS EC2 instances, it should also run in local k8s cluster as well. I am trying it locally for testing purposes.</p>
<p>Heres what I have tried so far but it is not working.</p>
<ul>
<li>First I set up my local 2-node cluster using kubeadm</li>
<li>Then I modified the installation script of the project (link given above) by removing all the references to EC2 (as I am using local machines) and kops (particularly in their create_cluster.py script) state.</li>
<li>I have modified their application yaml files (app requirements) to meet my localsetup (2-node)</li>
</ul>
<p>Unfortunately, although most of the application pods are created and in running state, some other application pods are unable to create and therefore, I am not being able to run the whole application on my local cluster.</p>
<p>I appreciate your help.</p>

Md Abul Kalam Azad Azad
<p>The true answer, as <em>Rajan Panneer Selvam</em> said in his response, is that it depends, but I'd like to expand somewhat on his answer by saying that your application <em>should</em> run on <em>any</em> K8S cluster given that it provides the services that the application consumes. What you're doing is considered good practice to ensure that your application is portable, which is always a factor in non-trivial applications where simply upgrading a downstream service could be considered a change of environment/platform requiring portability (platform-independence).</p>
<p>To help you achieve this, you should be developing a 12-Factor Application (12-FA) or one of its more up-to-date derivatives (12-FA is getting a little dated now and many variations have been suggested, but mostly they're all good).</p>
<p>For example, if your application uses a database then it should use DB independent SQL or no-sql so that you can switch it out. In production, you may run on Oracle, but in your local environment you may use MySQL: your application should not care. The credentials and connection string should be passed to the application via the usual K8S techniques of secrets and config-maps to help you achieve this. And all logging should be sent to stdout (and stderr) so that you can use a log-shipping agent to send the logs somewhere more useful than a local filesystem.</p>
<p>If you run your app locally then you have to provide a surrogate for every 'platform' service that is provided in production, and this may mean switching out major components of what you consider to be your application but this is ok, it is meant to happen. You provide a platform that provides services to your application-layer. Switching from EC2 to local may mean reconfiguring the ingress controller to work without the ELB, or it may mean configuring kubernetes secrets to use local-storage for dev creds rather than AWS KMS. It may mean reconfiguring your persistent volume classes to use local storage rather than EBS. All of this is expected and right.</p>
<p>What you should not have to do is start editing microservices to work in the new environment. If you find yourself doing that then the application has made a factoring and layering error. Platform services should be provided to a set of microservices that use them, the microservices should not be aware of the implementation details of these services.</p>
<p>Of course, it is possible that you have some non-portable code in your system, for example, you may be using some Oracle-specific PL/SQL that can't be run elsewhere. This code should be extracted to config files and equivalents provided for each database you wish to run on. This isn't always possible, in which case you should abstract as much as possible into isolated services and you'll have to reimplement only those services on each new platform, which could still be time-consuming, but ultimately worth the effort for most non-trival systems.</p>
