Tags: Web Application Management

Quick Post! – Using NetScaler responder policies/actions and backup vServers to notify users of Service Downtime

NetScaler, as I am sure you are aware, is a superbly powerful Application Delivery Controller. One of the most useful features is the use of Responder Policies/Actions, and Backup vServers to indicate that a service is down or to provide access to an alternative service for end users.

Let’s say – you have a load balancer configured that balances two Web Servers, which you then present for users to access. This load balancer could be configured with monitoring to check the health of the Web Servers, and also to ensure that the servers are loaded evenly with requests.

But – what happens when both servers are down? Maybe you have scheduled patching, or there is a fault. Leaving users with a blank page or one that times out is never ideal, and letting them know there is a fault is always best. This is especially relevant if the users are accessing pages of a commercial nature – for example, “The Online shop will be back open at 2pm” is a lot better than a blank page.

Both of the options below take less than 10 minutes configuration on a NetScaler – so if you need to get a page up quickly… these are very useful!

To do this – we can go down one of the two routes below:

Option 1

Use the Redirect URL option on the vServer – this redirects client requests to the custom URL when the service is down. So for example this could be a custom page on elsewhere, which explains that there is an issue.

This could be used for Scheduled patching for example – for times when we know the site will be down, we just add the URL to the vServer and any users who visit during the maintenance window will see the redirected page.

Option 2

Another option, is to use the Backup vServer feature within NetScaler – this is great because it can be used to direct traffic to a backup Data Center if our primary is unavailable. But also – we can use this feature to put up a NetScaler generated page informing the user that there is a problem with the backend service.

To do this – we need to create a new vServer to use for Maintenance. Create this with the following basic settings:

Then create a service for this – any local service bound to will do. Assign a basic monitor so that the service shows as up.

Next – go to AppExpert, and then Responder, and create a Responder Action. Fill out the details as below – note: you will need to create a new HTML Page, this is the 2nd and 3rd screenshots below:

HTML Page:

Click on Done, and then Click Create for the Responder Action.

We can then go back to the vServer and assign this under the Policies option. Select the options as per the screenshot below and press Continue:

Next we are presented with the below screen, click on the Plus sign next to “Select Policy”:

Fill out the details as per the below:

Click on “Create” and then click on “Bind”. Finally, click “Done”. We can now apply this vServer as a backup vServer to others – so that if those vServers are down, this page will be shown to users.

This is configured on a per vServer basis as per the below:

Now when accessing the page, and with the services down – the following page is shown:

Obviously, you can customise the page a little more than I have – but hopefully this will help. It’s a quick step to setup and gives some extra information to users when there is scheduled work or an unexpected fault.