Private Maps: Do I Need to Install My Own OSM Server?

There are many different ways to create "private maps" and depending on your exact needs different technological solutions are best suited to your situation. Therefore without knowing the exact circumstances it is difficult to say what you will need, but I can try and clarify some things that might help you choose better what is appropriate for your situation:

The rails_port server is (simplified) the web application running on OpenStreetMap.org, providing the website, user management, diaries and the editing API. It is not responsible for rendering and displaying the map tiles. Therefore the rails_port is nearly always not what people want, except for if you want to run your own private crowd sourced geodata project.

More commonly is that people need a "tile server", i.e. a server that takes the raw (XML) data provided by OpenStreetMap and turns it into bitmap renderings of a pretty map. Both Mapnik and Maperative are two of the common map rendering software that can be used for this task.

Maperative is a more integrative software package that covers tasks from designing stylesheets to actually rendering and tile serving. It also works well on Windows. Mapnik is only a rendering library and needs a whole host of additional software components e.g. mod_tile, tirex, postgresql. However mapnik and its corresponding tool chain is believed to scale better. So from what I have seen, Maperative tends to be used more if one only needs to render a small area, e.g. a city or wants to experiment with things. Mapnik with its toolchain is instead used commonly when setting up tile servers with a world wide map coverage like e.g. the one presented on osm.org.

Whether you need to set up any tile server depends on your usage amount and service requirements. Unlike for Google maps or Bing maps, nothing in the terms and conditions restrict your usage of the openstreetmap.org tile server to public facing usage. So private usage is theoretically fine (as long as you observe the license conditions of the data, but if you are using independent overlays rather than mixing the data that is probably the case). However, the reason why most people suggest to set up your own tile server for projects like this is the following:

The OpenStreetMap.org servers are entirely run on donated resources and have a fairly limited capacity. They cannot provide large scale tile serving and thus there are heavy restrictions on how much one is allowed to use them, irrespective of how you use them. As it is not a commercial service, it is not really specified how much exactly is allowed, but instead the rule of thumb is that if the sysadmins notice that a single user uses a significant amount of total available server resource that is too much and counter measures are put in place to limit the resource drainage. Furthermore, there is no up time guarantee and it can happen that the OpenStreetMap.org tile servers are down for several days for maintenance.

Due to those reasons it is generally encouraged for (commercial) projects of any significant size to not use the OpenStreetMap.org tile serving infrastructure and instead use ones own server infrastructure or one of the commercial osm tiles server providers for which one can get a performance and uptime guarantee. However, for small, non critical projects it might just be fine.

Having ones own tileserver however has additional advantages. E.g. one can design ones own map style that fits to the application in mind much better than a generic mapstyle.

You can find some additional resources on how to set up your own tileserver on http://switch2osm.org/