Stateful applications are applications that maintain client information in your area and employ the data for future transactions in the same client. These applications expect the customer to reconnect towards the same application instance, even if proxies or load balancers are introduced in the centre. Citrix ADC achieves this with the persistence feature supplied by the burden balancing (LB) virtual server. A vintage illustration of a persistence use situation? Application proprietors using HTTP cookies to provide a customized experience to individual finish users.
Within our last blog publish we checked out using Citrix ADC for canary deployments. Are you aware that you can use a canary deployment technique for stateful applications, too? You need to be careful, though. Adopting a canary deployment strategy here can result in disruptions since it can break the persistence, that is a key requirement of the fundamental functioning of stateful applications. Keep studying to learn to use Citrix ADC to apply canary deployment for stateful applications.
Filling the “Stickiness Gap”
Citrix ADC provides stickiness for stateful applications with the persistence feature in the LB vserver, although not in the content switching (CS) vserver. Because canary deployments focus on the CS vserver, there's been not a way to affiliate formerly connected client towards the same back-finish deployment (the LB vserver).
Using the discharge of Citrix ADC 13., this persistence feature is supported in the CS vserver entity, helping fill the “stickiness gap” between your client along with a particular deployment for stateful applications. Whenever a latest version of the application is released and brought to production, the persistence feature helps to ensure that the present client transactions aren't forwarded to the brand new canary version. Only part of the new client transactions is forwarded to canary version.
Similarly, following a new client is routed to particular version, when the same client reconnects back, it ought to keep to the same version and cannot assess the content switching policies again. Persistence overrides the information switching decision. To configure persistence on CS vserver, make use of the following command:
set cs vserver <name> -PersistenceType <type> [-timeout <integer>]
When the application monitoring returns a “failure” for that canary version, configurations akin to the newer version need to be taken off Citrix ADC. For stateful applications, these changes can’t be achieved abruptly simply because they can lead to disruptions which are visible towards the user.
Citrix recommends that you employ a website-based service group to represent the rear-finish group of cases of a specific version. In so doing, once the user (or container orchestrator) decommissions the rear-finish instances, the related entities on Citrix ADC are removed graciously. The entities aren't taken off Citrix ADC before the client transaction is finished. This permits seamless adoption of the canary deployment without disruptions towards the consumer experience. Citrix recommends enabling DNS-based autoscale around the service group while using following command:
add serviceGroup <serviceGroupName> -autoScale (YES NO)
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