I have a question on WSO2 API Manager Clustering. I have gone through the deployment documentation in detail and understand the distributed deployment concept where in one can seggregate the publisher, store, key manager and gateway. But as per my asessment, that makes the deployment architecture pretty complex to maintain. So I would like to have a simpler deployment.
What I have tested is to simply have two different instances of the WSO2 API Manager to run in two different boxes pointing to the same underlying data sources in MySQL. What I have seen is that, the API calls work perfectly and the tokens obtained from one WSO2 instance would work for API invocation on the other API Manager instance. The only issue with this model is that we need to deploy the APIs from individual publisher components for as many WSO2 API Manager instances that are running. I am fine to do that since the publishing will be done by one single small team. We will have a hardware load balancer in front having the API endpoint URLs and token endpoint URLs for both the API managers and the harware LB will do the load balancing.
So my question is - are there any problems in following this simple approach from the RUNTIME perspective? Does the clustering add any benefit from RUNTIME perspective for WSO2 API Manager?
Thank you.
Your approach has following drawbacks (there can be more which I do not know);
Distributed throttling won't work. It will lead to throttling inconsistencies since the throttling replication won't happen if you don't enable clustering. Lets say you define 'Gold' tier for an API. Doesn't matter how many gateway instances you are using, a user should be restricted to access no more than 20req/min to this API. This should have been implemented based on a distributed counter (not sure the exact implementation details). So if you don't enable clustering, one gateway node doesn't know the number of requests served by other gateway nodes. So each gateway node will have their own throttle counter. Meaning - a user might be able to access your API more than 20req/min. So this is one of the throttling inconsistencies. Further, lets say one gateway node is throttled out a user but the other gateway node is not. Now, if your LB routes the request to 1st gateway node, user will not be able to access the API. If your LB routes the request to 2nd gateway node, user will be able to access the API. This is another instance of throttling inconsistency. To overcome all these issues, you just need to replicate the throttling across all the gateway nodes by enabling clustering.
Distributed caching won't work. For example, API Key validation information are cached. If you revoke a token in one API Manager node, cache will be cleared in that node. So a user can't use revoked token via that API Manager node, BUT he is able to use the token via the other API Manager node until the cache is invalidated (I guess 15 min by default). This is just one instance where things can go wrong if you don't cluster your API Manager instances. To solve these issues, you just need to enable clustering, then the cache will be in sync across the cluster. Read this doc for more details on various caching available in WSO2 API Manager.
You will be having several issues if you don't have above features. WSO2 highly recommends distributed deployment in production.