Stateful failover for IP Security (IPsec) enables a router to continue processing and forwarding IPsec packets after a planned or unplanned outage occurs. Customers employ a backup (secondary) router that automatically takes over the tasks of the active (primary) router if the active router loses connectivity for any reason. This failover process is transparent to users and does not require adjustment or reconfiguration of any remote peer.
Stateful failover for IPsec requires that your network contains two identical routers that are available to be either the primary or secondary device. Both routers should be the same type of device, have the same CPU and memory, and have either no encryption accelerator or identical encryption accelerators.
Prerequisites for Stateful Failover for IPsec
Complete, Duplicate IPsec and IKE Configuration on the Active and Standby Devices This document assumes that you have a complete IKE and IPsec configuration. The IKE and IPsec configuration that is set up on the active device must be duplicated on the standby device. That is, the crypto configuration must be identical with respect to Internet Security Association and Key Management Protocol (ISAKMP) policy, ISAKMP keys (preshared), IPsec profiles, IPsec transform sets, all crypto map sets that are used for stateful failover, all access control lists (ACLs) that are used in match address statements on crypto map sets, all AAA configurations used for crypto, client configuration groups, IP local pools used for crypto, and ISAKMP profiles. Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_vpnav/configuration/15-mt/sec-vpnavailability-15-mt-book/sec-state-fail-ipsec.html Although the prerequisites only stated that "Both routers should be the same type of device" but in the "Restrictions for Stateful Failover for IPsec" section of the link above, it requires "Both the active and standby devices must run the identical version of the Cisco IOS software" so answer E is better than answer B.
This document assumes that you have a complete IKE and IPsec configuration.
The IKE and IPsec configuration that is set up on the active device must be duplicated on the standby device.
That is, the crypto configuration must be identical with respect to Internet Security Association and Key Management Protocol (ISAKMP) policy, ISAKMP keys (preshared), IPsec profiles, IPsec transform sets, all crypto map sets that are used for stateful failover, all access control lists (ACLs) that are used in match address statements on crypto map sets, all AAA configurations used for crypto, client configuration groups, IP local pools used for crypto, and ISAKMP profiles.
Reference:
Although the prerequisites only stated that "Both routers should be the same type of device" but in the Complete, Duplicate IPsec and IKE Configuration on the Active and Standby Devices This document assumes that you have a complete IKE and IPsec configuration. The IKE and IPsec configuration that is set up on the active device must be duplicated on the standby device. That is, the crypto configuration must be identical with respect to Internet Security Association and Key Management Protocol (ISAKMP) policy, ISAKMP keys (preshared), IPsec profiles, IPsec transform sets, all crypto map sets that are used for stateful failover, all access control lists (ACLs) that are used in match address statements on crypto map sets, all AAA configurations used for crypto, client configuration groups, IP local pools used for crypto, and ISAKMP profiles. Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_vpnav/configuration/15-mt/sec-vpnavailability-15-mt-book/sec-state-fail-ipsec.html Although the prerequisites only stated that "Both routers should be the same type of device" but in the "Restrictions for Stateful Failover for IPsec" section of the link above, it requires "Both the active and standby devices must run the identical version of the Cisco IOS software" so answer E is better than answer B.

Explanation
In this IaaS model, cloud providers offer resources to users/machines that include computers as virtual machines, raw (block) storage, firewalls, load balancers, and network devices.
Note: Cloud access security broker (CASB) provides visibility and compliance checks, protects data against misuse and exfiltration, and provides threat protections against malware such as ransomware.

Northbound APIs are the link between the applications and the SDN controller. The applications can tell the network what they need (data, storage, bandwidth, and so on) and the network can deliver those resources, or communicate what it has. These APIs support a wide variety of applications, such as load balancers, firewalls, orchestration platforms, and automation stacks. Northbound APIs also enable the applications to use the controller's capabilities to program flows into the network devices using the southbound interface. Northbound APIs are usually RESTful APIs that use HTTP methods to exchange data in JSON or XML formats12.
OpenFlow is not a northbound API protocol, but a southbound API protocol that defines the communication between the SDN controller and the network switches or routers. OpenFlow allows the controller to manipulate the forwarding behavior of the switches or routers by sending commands and receiving events3 .
NETCONF is not a northbound API protocol, but a network management protocol that can be used as a southbound API protocol to configure and monitor network devices. NETCONF uses XML to encode data and remote procedure calls (RPCs) to exchange messages between the controller and the network devices
. References := 1: What are SDN Northbound APIs (and SDN Rest APIs)? - SDxCentral 2: SDN North-bound and South-bound APIs and Interfaces 3: OpenFlow - Wikipedia : OpenFlow - SDxCentral : NETCONF - Wikipedia : NETCONF Protocol - Cisco
1sdxcentral.com2computernetworkingnotes.com3examguides.com