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Live Guard High Availability

With Live Guard High Availability, we aim to adjust to any network situation in such a manner that we provide the most possible functionalities at any given moment.

How does it work?

In an ideal world, your devices and applications are always able to reach EVA Cloud.

This will not always be the case though, so Live Guard provides two possible fallbacks;

  1. A very lightweight EVA instance running on your Watchtower device. This 'EVA Lightweight' can take over whenever you lose connection to the internet or EVA. We call this Offline mode.
  2. A Live Guard module in our applications that caches certain information like products and the current order.

If EVA Cloud is unreachable, either because EVA is down or you have no internet, Offline mode kicks in. That is, if your local Watchtower device can be reached. If Watchtower is also unavailable, the Live Guard module in your application takes over.

Offline mode

While in Offline mode, we allow for order creation, assembly and checkout using cash and custom payment methods. Products are available, as well as a local order history, albeit in a slimmed-down manner. We also allow for manual discounts, refunds and price overrides, markdown prices and PIN logins.

Some additional functionalities remain available when just EVA Cloud is down, but you are still connected to the internet. Because it's just EVA that's down, we can still perform PIN payments through external PSP's. We also allow external gift- and loyalty cards to be used and we can use AvaTax to perform tax calculations.

Live Guard Module fallback mode

When your applications can't reach EVA Cloud, nor Watchtower, we've got ourselves a little situation.

When we have to fall back to the Live Guard module in the application itself, we just store your current order information so we can pick up where we left off when the connection to either Watchtower or EVA Cloud is restored. In this scenario it remains impossible to process orders. Consider this fallback somewhat of an 'anti stall'.

When is EVA Cloud considered unreachable?

Watchtower pings the internet and EVA Cloud every minute. As soon as a ping fails to generate a response, Watchtower will urge the POS and Companion Apps to connect with Watchtower instead of the internet. This transition from EVA Cloud to your local Watchtower is seamless and invisible to users. The current order is always known on the device, so the user can continue working on the order as if nothing happened.

During this offline mode, Watchtower logs all events in order to later sync these events when the connection to EVA Cloud is restored.

Going back online

During offline mode, Watchtower keeps pinging EVA and the internet every minute. As soon as the ping returns a response three consecutive times, all devices connect to EVA Cloud again, and Watchtower makes sure to correctly synchronize all offline events towards EVA Cloud.

Forcing offline mode

In case your internet is super wonky, but Watchtower manages to ping successfully now and then, offline mode will not trigger. In that case, you might want to force offline mode. To do so, set the setting Sentinel:ForceEVACloudUnavailable to true.