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In Azure all Virtual machines can be deployed as part of an Availability Set. This will assure that VMs that are part of the same Availability Set won’t be affected at the same time by Azure maintenance, windows updates etc.
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Master Controller
There can only be one Master Controller running at a time and is a single point of failure. This can only be avoided by deploying a dual MC system. Probably starting with Delft-FEWS 2022.02 multiple Master Controllers can be run on one database.
As a result of this, the Master Controller cannot be scaled horizontally. Since the Master Controller is a single point of failure, it is important to monitor the health of the Master Controller.
Scaling the Master Controller vertically can be done by redeploying the Master Controller.
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Forecasting Shell Servers
Forecasting Shell Servers can be scaled up both horizontally and vertically.
Scale horizontally: deploying a new Forecasting Shell Server virtual machine for an FSS Group that needs more forecasting shells.
Scale vertically: update an existing Forecasting Shell Server Virtual Machine with more resources. To allow a Forecasting Shell to use more memory, the Delft-FEWS FSS client config file can be customized. It is also possible to run multiple Forecasting Shells on the same Virtual machine.
Deploying multiple Forecasting Shell Servers will avoid a single point of failure.
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Admin Interface
The Admin Interface can be scaled up both horizontally and vertically.
Scale horizontally: deploying a new Admin Interface virtual machine. A load balancer or application gateway is used in front of the Admin Interface and new VMs must be registered with the loadbalancer.
Scale vertically: update an existing Admin Interface Virtual Machine with more resources.
Deploying multiple Admin Interfaces will avoid a single point of failure.
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Web Services
The Web Services can be scaled up both horizontally and vertically.
Scale horizontally: deploying a new Web Services ARM template. A load balancer or application gateway is used in front of the Web Services and new VMs must be registered with the loadbalancer.
Scale vertically: Redeploy the Web Services Virtual Machine with more resources.
Deploying multiple Web Services will avoid a single point of failure.
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Archive Server
The Archive Server can be scaled up both horizontally and vertically, but more manual actions are required.
Scale horizontally: Deploy a new Archive Server Virtual Machine. A load balancer or application gateway is used in front of the Archive and new VMs must be registered with the loadbalancer.
The scheduling of the harvester must be duplicated to the new VM. Since the harvester builds the index it takes some time before a new archive server is in sync. The load balancer should use sticky sessions to make sure consistent results are given all the time for the same user.
Scale vertically: Redeploy the Archive Server Virtual Machine with more resources.
Deploying multiple archive servers will avoid a single point of failure.
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The Operator Client provides some access to information on the status of the system components, file imports and workflows.
Admin Interface
The Web Based Delft-FEWS Admin Interface provides a dashboard for the FEWS Administrators to view the status of the Delft-FEWS components and workflows. Errors and events are logged within the central database and log extracts can be downloaded via the browser to provide to Deltares in the event of issues which can't be resolved internally.
The Admin Interface also provides a series of APIs to enable access to the events and status information and the audit logs.
Audit Logs of user actions are also stored in the central database and the Admin Interface API can be used to access these events.
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