Cloud Services
This domain tests the provisioning, networking, elasticity, and data-protection behavior of cloud services on Huawei Cloud and Huawei Cloud Stack. Questions typically combine ECS, EVS, VPC, ELB, AS, OBS, and RDS into a small architecture scenario.
Core rules
- ECS placement depends on AZ, flavor, image, and affinity/anti-affinity groups. Anti-affinity spreads instances across hosts for availability.
- EVS volumes are AZ-scoped. Snapshots protect volume data; backups protect entire servers and can be used for restoration.
- VPC provides subnets, route tables, security groups, and network ACLs. Security groups are stateful; ACLs are stateless and evaluated in order.
- ELB listeners forward to backend server groups and use health checks to remove unhealthy backends.
- AS adds or removes ECS instances based on policies, with a cooldown to prevent rapid fluctuation.
- OBS uses buckets and policies/ACLs; RDS supports primary/standby HA and read replicas.
Worked example
A web tier must survive an AZ outage and scale with traffic. Reasoning: deploy ECS instances in at least two AZs behind an ELB, use an anti-affinity group within each AZ, and attach an AS policy with a cooldown. Put the database on RDS primary/standby across AZs. The ELB health check must target the application port, not just ICMP. If the AS scale-out is too slow, check the cooldown and warm-up settings before increasing the maximum instance count.
Traps that cost marks
- Thinking an EVS volume can attach across AZs; it cannot.
- Confusing security groups with network ACLs: ACLs are stateless.
- Setting an ELB health check to the wrong port, causing healthy backends to be removed.
- Assuming AS immediately reacts; cooldown and warm-up delay scaling.
Key points
- ECS availability depends on AZ, anti-affinity, and flavor capacity.
- EVS is AZ-scoped; snapshots and backups serve different recovery scopes.
- Security groups are stateful; network ACLs are stateless.
- ELB health checks determine backend availability.
- AS scaling is governed by policies, cooldown, and warm-up.