Tomcat: Change the Virtual hosts programmatically?

Question

Hello,

Tomcat offers a build in "Virtual Hosting" Support: An Engine/Web-Application can be configured to be responsible for a list of Domains. These Domains have to be put into the server.xml/context.xml files with a special xml directive.

=> Is there any possibility to change the Tomcat Configuration (in general) and especially the "Virtual Hosts" of a Web-Application/Engine programmatically?

For example if a new user signs up, I have to add his domain to the list of "accepted virtual hosts/domains". The only way I currently think of is changing the xml files via a script and then restart Tomcat.

Is there any way to add them add runtime via some Java-Methods programmatically?

Thank you very much! Jan

Answer 1

I would suggest you set your application to be the default virtual host in server.xml so your single virtual host can respond to requests addressed to any host name. Tomcat ships with the localhost application set as the default virtual host. So you can see how to do this by simply inspecting the server.xml file of a vanilla tomcat installation. You can programatically determine the host name the user sent the request to using the ServletRequest.getServerName() method.

Tomcat used to ship with a web application called "host-manager". Note: this is different than the "manager" web application that still comes with Tomcat. Host manager allowed for changing configuration or adding new virtual hosts on the fly without restarting the server. You could interact with the host-manager over HTTP (programmatically if desired). However, it had the unfortunate flaw of not committing its changes to server.xml so they were all lost on a web server restart. For whatever reason, starting with version 6, Tomcat no longer ships with the host-manager application. So it doesn't appear to be supported anymore.

Answer 2

You shouldn't change the server environment programmatically and there are no reliable and standard ways to do this. Best is to do and keep it all on the webapp side. To start, a Filter is perfectly suitable for this. Store the names somewhere in a database table or a properties file which you cache in the application scope. Check the HttpServletRequest#getRequestURI() (or the getServerName() if it is a subdomain instead of pathinfo) and do the forwarding task accordingly.

Hope this helps.

Answer 3

Tomcat provides APIs to create new virtual host. To get access to the wrapper object needed for this, you need to implement a ContainerServlet. You can create virtual host like this,

    Context context = (Context) wrapper.getParent();
    Host currentHost = (Host) context.getParent();
    Engine engine = (Engine) currentHost.getParent();

    StandardHost host = new StandardHost();
    host.setAppBase(appBase);
    host.setName(domainName);

    engine.addChild(host);

You need to make sure appBase directory exist and you have to find ways to persist the new host to the server.xml or you lose the host on restart.

However, this approach rarely works. If your users run their own apps, you really want run separate instances of Tomcat so you can sandbox the apps better. e.g. One app running out of memory doesn't kill all other apps.

If you provide the app, you can just use one host (defaultHost). You can get the domain name from Host header and do whatever domain-specific stuff in your code.