Multiple Site to Site VPN Tunnels on One Cisco Router
Example for Establishing an IPSec Tunnel Using a Tunnel Interface - AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010 CLI-based Configuration Guide - VPN - Huawei
IPSec Stateful Failover (VPN High Availability) Feature Module - Cisco
Manual:IP/IPsec - MikroTik Wiki
IPsec Configuration Guide, Cisco IOS XE 17 (Cisco ASR 900 Series) - Overview of IPsec [Cisco ASR 900 Series Aggregation Services Routers] - Cisco
Two ways to have redundancy with IPSEC tunnels – IoSonoUnRouter