Node Switcher UI Page!
If you aren’t familiar, when you log into ServiceNow, you are assigned a node dynamically, to serve all your transactions. There many be many situations where you may want to switch to a different node. There isn’t any functionality available to the general public for this (though I know you exist hop2node!)
I developed my own node switching tool as an alternative to Chrome Extensions, since many companies have security restrictions for those. This page instead acts as a native tool within ServiceNow!
A number of you might be wondering how I was able to get this to actually work…. Or even if you aren’t I’m here to explain anyways!
Step 1 - Figuring out how to get the node IP address cookie value for all nodes. For this I had two big hints:
This little tool on the ServiceNow Share: Generate Node BigIP - Switch Between ServiceNow Nodes
This gave me the biggest hint, that part of nodes name on typical deployments, includes the last numbers for the IP address of that node. That saves so much time from a lookup perspective, since you just need to get the ballpark initial parts of the IP address first, since the nodes should be in the same data center.
The next part, which is the even harder part, most tools make use of querying stats.do to get the node IP address. However, that page is pretty long, parsing it isn’t as reliable, and most security advise is to lock down that page. I got a tip from Ahmed Hmeid from ServiceNow Gems to use SOAP against InstanceInfo.do. This is the same way the MID servers get the instance details. Basically just have to spoof a MID server!
Step 2 - Figuring out what the user’s current node is. This part was also harder than I expected. The value of the node stored in the cookie is an HTTP only flag cookie, which means it can’t be read client side at all. However, there are two server side workarounds!
var request = GlideTransaction.get().getRequest();
result.user.node_cookie = GlideCookieMan.getCookieValue(request.getCookies(), 'BIGipServerpool_' + this.instanceName);
result.user.node_name = (GlideServlet.getSystemID() + '').split(':')[1]; //get the second half of the node name
Step 3 - Mechanism for switching the node. Since it’s a special cookie, you can’t just use any normal client side function to change it. I found out though after a bit of digging, that Processors have the ability to write cookies! There is an undocumented function called g_response.addCookie which can set and override even HTTP only cookies.
var cookie = new Packages.javax.servlet.http.Cookie('BIGipServerpool_' + instanceName, node_id);
cookie.setPath("/");
g_response.addCookie(cookie);
All together the flow looks like this: UI Page Pre-Load > Script Include > SOAP > UI Page > Processor > UI Page. I’ve also added some other data enrichment in the script include to grab node metrics as well.
Closing Thoughts
I hope to one day package this up and post it on the ServiceNow share. Just a couple more things I have to get cleared up first (like getting it to work with other node naming conventions, simplifying the MID server user requirement, etc.). Developing this tool was quite the ride and challenge, but I’m happy with the result!