CompTIA A+ Exam > CompTIA A+ Notes > Cheatsheet: Virtualisation & Cloud Computing
Cheatsheet: Virtualisation & Cloud Computing
1. Virtualisation Fundamentals
1.1 Core Concepts
| Term | Definition |
|---|---|
| Virtualisation | Technology that allows multiple operating systems to run simultaneously on a single physical machine |
| Hypervisor | Software layer that creates and manages virtual machines |
| Virtual Machine (VM) | Self-contained software environment that emulates a complete physical computer |
| Host Machine | Physical computer running the hypervisor and hosting virtual machines |
| Guest OS | Operating system installed within a virtual machine |
1.2 Hypervisor Types
| Type | Characteristics |
|---|---|
| Type 1 (Bare Metal) | Runs directly on hardware; higher performance; examples: VMware ESXi, Microsoft Hyper-V, Citrix XenServer |
| Type 2 (Hosted) | Runs on top of host OS; easier to set up; examples: VMware Workstation, Oracle VirtualBox, Parallels Desktop |
1.3 Resource Requirements
- CPU: Must support hardware-assisted virtualisation (Intel VT-x or AMD-V)
- RAM: Sufficient memory for host OS plus all guest VMs combined
- Storage: Adequate disk space for virtual disk files (VHD, VHDX, VMDK)
- Network: Virtual switches and NICs for VM connectivity
2. Virtual Machine Components
2.1 Virtual Hardware
| Component | Description |
|---|---|
| Virtual CPU (vCPU) | Abstracted processor allocated to VM from physical CPU cores |
| Virtual RAM | Memory allocated from host physical RAM to guest VM |
| Virtual Disk | File-based storage (VHD, VHDX, VMDK) that emulates physical hard drive |
| Virtual NIC | Emulated network adapter providing network connectivity to VM |
| Virtual GPU | Emulated graphics adapter for display output |
2.2 VM Configuration Files
| File Type | Purpose |
|---|---|
| .vmx (VMware) | VM configuration file containing hardware settings |
| .vmdk (VMware) | Virtual disk file storing VM data |
| .vhd / .vhdx (Hyper-V) | Virtual hard disk files for Microsoft environments |
| .ova / .ovf | Open Virtualisation Format for VM portability between platforms |
2.3 Network Modes
| Mode | Behavior |
|---|---|
| Bridged | VM connects directly to physical network; receives own IP from network DHCP |
| NAT | VM shares host IP address; isolated from physical network but has internet access |
| Host-Only | VM communicates only with host and other VMs; no external network access |
| Internal | VM communicates only with other VMs on same virtual network |
3. Cloud Computing Models
3.1 Service Models
| Model | Description |
|---|---|
| IaaS (Infrastructure as a Service) | Provides virtualised computing resources (VMs, storage, networks); customer manages OS and applications; examples: AWS EC2, Azure Virtual Machines |
| PaaS (Platform as a Service) | Provides platform for application development and deployment; provider manages infrastructure and OS; examples: Azure App Service, Google App Engine |
| SaaS (Software as a Service) | Provides complete applications over internet; provider manages everything; examples: Microsoft 365, Salesforce, Google Workspace |
3.2 Deployment Models
| Model | Characteristics |
|---|---|
| Public Cloud | Services offered over public internet; multi-tenant; cost-effective; examples: AWS, Azure, Google Cloud |
| Private Cloud | Dedicated infrastructure for single organisation; higher security and control; on-premises or hosted |
| Hybrid Cloud | Combination of public and private clouds; data and applications shared between them |
| Community Cloud | Shared infrastructure for specific community with common concerns |
3.3 Cloud Characteristics
- On-demand self-service: Users provision resources without human interaction
- Broad network access: Services available over network via standard mechanisms
- Resource pooling: Multi-tenant model with resources dynamically assigned
- Rapid elasticity: Scale resources up or down quickly based on demand
- Measured service: Pay-per-use billing model with resource monitoring
4. Cloud Service Components
4.1 Compute Services
| Service | Description |
|---|---|
| Virtual Machines | On-demand computing instances with configurable CPU, RAM, storage |
| Containers | Lightweight application packaging; share host OS kernel; examples: Docker, Kubernetes |
| Serverless Computing | Run code without managing servers; automatic scaling; pay per execution; examples: AWS Lambda, Azure Functions |
4.2 Storage Services
| Type | Use Case |
|---|---|
| Object Storage | Unstructured data storage with HTTP access; examples: AWS S3, Azure Blob Storage |
| Block Storage | Raw storage volumes for VMs; low-latency; examples: AWS EBS, Azure Managed Disks |
| File Storage | Network file shares accessible via SMB/NFS; examples: AWS EFS, Azure Files |
4.3 Network Services
- Virtual Private Cloud (VPC): Isolated network environment within cloud
- Load Balancer: Distributes traffic across multiple instances
- Content Delivery Network (CDN): Caches content at edge locations for faster delivery
- VPN Gateway: Secure connection between on-premises and cloud networks
- DNS Services: Domain name resolution and traffic management
5. Virtualisation Security
5.1 Security Considerations
| Area | Best Practices |
|---|---|
| VM Isolation | Ensure VMs cannot access each other's memory or resources; prevent VM escape attacks |
| Hypervisor Security | Keep hypervisor patched and updated; minimize attack surface; restrict management access |
| Network Segmentation | Use VLANs and virtual switches to separate VM traffic; implement firewall rules |
| Patch Management | Update guest OS, applications, and hypervisor regularly |
5.2 VM Sprawl Prevention
- Implement VM lifecycle policies and governance
- Regular inventory audits to identify unused VMs
- Automated decommissioning of idle resources
- Resource quotas and approval workflows
- Documentation and naming conventions
5.3 Cloud Security
| Concept | Description |
|---|---|
| Shared Responsibility Model | Provider secures infrastructure; customer secures data, applications, access controls |
| Identity and Access Management (IAM) | Control who can access resources and what actions they can perform |
| Encryption | Data at rest and in transit encryption; key management services |
| Multi-Factor Authentication (MFA) | Additional authentication layer beyond username and password |
6. Virtualisation Management
6.1 VM Operations
| Operation | Description |
|---|---|
| Snapshot | Point-in-time copy of VM state including memory, settings, and disk; used for backups and rollback |
| Clone | Complete copy of VM creating independent duplicate |
| Template | Master copy of VM used to deploy multiple identical instances |
| Migration | Moving VM from one host to another; live migration allows zero downtime |
| P2V (Physical to Virtual) | Converting physical machine to virtual machine |
| V2V (Virtual to Virtual) | Converting VM from one hypervisor format to another |
6.2 Resource Allocation
| Technique | Purpose |
|---|---|
| Resource Pooling | Aggregating physical resources for allocation to VMs |
| Overcommitment | Allocating more virtual resources than physical capacity; works when VMs don't use full allocation |
| Reservation | Guaranteed minimum resources allocated to VM |
| Limit | Maximum resources VM can consume |
| Shares | Relative priority for resource allocation during contention |
6.3 High Availability Features
- Clustering: Multiple hosts working together for redundancy
- Fault Tolerance: Duplicate VM running in lockstep on separate host
- Automatic Restart: VM automatically restarts on another host after failure
- Load Balancing: Distribute VMs across hosts based on resource usage
- DRS (Distributed Resource Scheduler): Automatic VM placement and migration for optimal performance
7. Cloud Management & Monitoring
7.1 Management Tools
| Tool Type | Function |
|---|---|
| Cloud Management Console | Web-based interface for provisioning and managing cloud resources |
| Command Line Interface (CLI) | Script-based resource management; examples: AWS CLI, Azure CLI |
| Infrastructure as Code (IaC) | Define infrastructure using code; examples: Terraform, CloudFormation |
| Orchestration Tools | Automate deployment and configuration; examples: Ansible, Puppet, Chef |
7.2 Monitoring & Metrics
- CPU utilisation: Percentage of compute capacity used
- Memory usage: RAM consumption and available memory
- Disk I/O: Read/write operations per second and throughput
- Network throughput: Bandwidth usage and packet rates
- Response time: Application performance and latency
- Availability: Uptime percentage and SLA compliance
7.3 Cost Management
| Strategy | Description |
|---|---|
| Right-Sizing | Match resource allocation to actual usage needs |
| Reserved Instances | Commit to long-term usage for discounted rates |
| Auto-Scaling | Automatically adjust resources based on demand |
| Spot Instances | Use spare capacity at reduced cost for non-critical workloads |
| Resource Tagging | Label resources for cost tracking and allocation |
8. Desktop Virtualisation
8.1 VDI (Virtual Desktop Infrastructure)
| Component | Description |
|---|---|
| VDI | Centralised desktop hosting where each user gets dedicated VM; examples: VMware Horizon, Citrix Virtual Apps and Desktops |
| Connection Broker | Manages user authentication and desktop assignment |
| Thin Client | Lightweight hardware device used to access virtual desktop |
| Remote Display Protocol | Transmits desktop interface to client; examples: RDP, PCoIP, Blast Extreme |
8.2 VDI Deployment Models
| Model | Characteristics |
|---|---|
| Persistent VDI | User assigned same VM each session; customisations retained; higher storage requirements |
| Non-Persistent VDI | User gets generic VM from pool; changes discarded after logout; lower storage needs |
8.3 Application Virtualisation
- Isolates applications from underlying OS
- Applications run in sandboxed environment
- Eliminates conflicts between applications
- Simplifies deployment and updates
- Examples: Microsoft App-V, VMware ThinApp, Citrix XenApp
9. Backup & Disaster Recovery
9.1 Backup Strategies
| Method | Description |
|---|---|
| Full Backup | Complete copy of all data; longest time and storage; fastest restore |
| Incremental Backup | Only changes since last backup; fastest backup; slower restore |
| Differential Backup | Changes since last full backup; moderate backup time; faster restore than incremental |
| Image-Level Backup | Entire VM captured as single file; application-consistent backups |
9.2 Recovery Metrics
| Metric | Definition |
|---|---|
| RTO (Recovery Time Objective) | Maximum acceptable downtime after disaster |
| RPO (Recovery Point Objective) | Maximum acceptable data loss measured in time |
9.3 Cloud Backup Options
- Cloud-to-cloud backup: Protect SaaS data to separate cloud storage
- Hybrid backup: Local backups replicated to cloud
- Cloud storage tiers: Hot (frequent access), Cool (infrequent), Archive (long-term)
- Geographic redundancy: Data replicated across multiple regions
- Versioning: Multiple versions of files retained for recovery
9.4 Disaster Recovery Strategies
| Strategy | Characteristics |
|---|---|
| Hot Site | Fully operational duplicate environment; immediate failover; highest cost |
| Warm Site | Partial infrastructure ready; requires configuration before use; moderate cost |
| Cold Site | Empty facility with basic utilities; longest recovery time; lowest cost |
| Cloud DR | Failover to cloud environment; pay-per-use; scalable resources |
10. Performance Optimisation
10.1 VM Performance Tuning
- Allocate appropriate vCPU count (avoid overprovisioning)
- Configure adequate RAM to prevent memory swapping
- Use SSD storage for improved disk I/O
- Install guest tools/additions for enhanced drivers
- Disable unnecessary services in guest OS
- Use paravirtualised drivers for better performance
10.2 Storage Optimisation
| Technique | Benefit |
|---|---|
| Thin Provisioning | Allocate storage on demand; saves disk space; prevents over-allocation |
| Thick Provisioning | Pre-allocate full storage; better performance; guaranteed space |
| Deduplication | Eliminate duplicate data blocks; reduces storage requirements |
| Compression | Reduce data size; lowers storage costs; slight CPU overhead |
10.3 Network Optimisation
- Use multiple physical NICs for network redundancy
- Configure NIC teaming for load balancing
- Implement QoS (Quality of Service) for traffic prioritisation
- Separate management, VM, and storage networks
- Enable jumbo frames for large data transfers
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Apr 20, 2026 Last updated
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