Question: I have Ignite instance started as a 'server mode' on computer A, created cache in it and stored 1M Key->Values inside the cache.

Then I started Ignite instance as a 'server mode' on computer B which joined Ignite instance on computer A and now have a cluster of 2 nodes.

Is it possible to move all 1M K->V from computer A to computer B (without any interruption for querying data or ingesting data) so that computer A can be shut down for maintenance and everything continue to work from computer B?

If this is possible - what are the steps and code to do that (move data from A -> B)?

Answer: 
Ignite distributes data across server nodes according to [Cache Modes](https://apacheignite.readme.io/docs/cache-modes).

In `REPLICATED` mode each server holds a copy of all data, so you can shut down any node and data won't be lost.

In `PARTITIONED` mode you can set `CacheConfiguration.backups` to `1` (or more) so that data is evenly distributed across server nodes, but each server also holds a copy of data from some other server. In this scenario you can shut down any single node and data won't be lost.
There are the features named "backup" and "CacheRebalanceMode" of IgniteCache.I think you can try these.