AWS Cloud

You can navigate the AWS global infrastructure, manage accounts securely, and set up your foundational environment.

1. What cloud computing is: IaaS, PaaS and SaaS90 min
   • Shared responsibility model
   • Capex vs Opex financial models
   • Global infrastructure overview
   • Elasticity and pay-as-you-go pricing
   • Cloud native vs lift-and-shift strategies
2. AWS global infrastructure: regions, availability zones and edge locations90 min
   • Region selection criteria and data residency
   • AZ isolation, power redundancy, and fault domains
   • CloudFront edge locations and points of presence
   • Local zones and wavelength zones
   • Cross-region data transfer considerations
3. Creating and securing an AWS account, billing and the free tier2 hrs
   • Root account protection and hardware MFA enforcement
   • AWS Budgets and Cost Anomaly Detection
   • Cost Explorer filtering and tag-based allocation
   • Free tier limit tracking and alert thresholds
   • Consolidated billing and AWS Organizations setup
4. The AWS Management Console, CLI and SDKs2 hrs
   • aws configure command and credential files
   • Named profiles and SSO credential helpers
   • AWS CloudShell interactive terminal usage
   • Boto3 and AWS SDK client initialization
   • CLI pagination flags and output formatting with --query
5. The shared responsibility model and the Well-Architected Framework2 hrs
   • Security of the cloud vs security in the cloud
   • Six pillars of the AWS Well-Architected Framework
   • Operational excellence and design principles
   • Reliability trade-offs and disaster recovery targets
   • Sustainability and cost optimization pillars
6. Initial CLI operations and profile configuration90 min
   • aws sts get-caller-identity validation
   • IAM user access key generation and rotation
   • Environment variable precedence for credentials
   • Configuring region defaults in ~/.aws/config
   • Troubleshooting AccessDenied errors in CLI

Hands-on project: Provision a secure AWS account with billing alerts, root MFA, and a custom IAM administrative user using the AWS CLI v2 with named profiles.

You can construct precise IAM policies enforcing least privilege across users, groups, and service roles.

1. Users, groups, roles and policies90 min
   • JSON policy structure and syntax
   • Effect, Action, Resource, and Principal elements
   • Inline policies vs customer managed policies
   • AWS managed policies vs custom policies
   • IAM group membership management
2. Authentication and authorization explained90 min
   • STS assume-role API and session tokens
   • Policy evaluation logic and evaluation flow
   • Explicit deny precedence over explicit allow
   • Default deny baseline rule
   • Condition keys for source IP and TLS enforcement
3. IAM best practices and least privilege2 hrs
   • IAM Access Analyzer for policy validation
   • IAM credential reporting and last used tracking
   • Rotating access keys safely without downtime
   • Eliminating static credentials with IAM roles
   • Auditing wildcard permissions in production
4. MFA, access keys and roles for services90 min
   • Enforcing hardware and virtual MFA conditions
   • EC2 instance profiles and metadata service v2 (IMDSv2)
   • Temporary security credentials generation
   • Cross-account trust relationships and external IDs
   • Service roles for Lambda and CloudFormation
5. AWS Organizations and IAM Identity Center overview90 min
   • Multi-account management best practices
   • Service Control Policies (SCPs) inheritance
   • IAM Identity Center single sign-on configuration
   • Organizational unit (OU) hierarchy design
   • Tag policies and resource organization
6. Debugging IAM authorization failures90 min
   • aws iam simulate-principal-policy command
   • CloudTrail error analysis for Client.UnauthorizedOperation
   • Resource-based policies vs identity-based policies
   • Cross-account principal ARN validation
   • Boundary policies for delegated administration

Hands-on project: Create least-privilege IAM policies, configure cross-account roles, and attach service-linked roles for automated EC2 backups.

You can launch, secure, and elastically scale virtual server fleets behind load balancers.

1. EC2 instances, AMIs and instance types2 hrs
   • Compute-optimized c6i vs memory-optimized r6i families
   • Custom AMI creation with Packer and EC2 Image Builder
   • Spot instances, On-Demand, and Savings Plans trade-offs
   • Instance hibernation and stop/start lifecycle
   • Placement groups: cluster, spread, and partition
2. Key pairs, security groups and connecting to instances90 min
   • SSH key pair generation and public key uploading
   • Security group stateful inbound and outbound rules
   • EC2 Instance Connect and Session Manager (SSM)
   • Troubleshooting SSH connection timeouts
   • Referencing security group IDs as source rules
3. EBS volumes, snapshots and instance storage2 hrs
   • gp3 vs io2 Block Express volume types
   • EBS snapshot lifecycle policies with AWS Backup
   • Root volume encryption with AWS KMS
   • Extending file systems online after volume resizing
   • Ephemeral instance store performance characteristics
4. Elastic Load Balancing: ALB and NLB2 hrs
   • Target groups, health check intervals, and deregistration delays
   • Path-based and host-based routing rules on ALB
   • SSL/TLS certificate termination with AWS Certificate Manager (ACM)
   • Network Load Balancer (NLB) TCP passthrough and static IPs
   • Cross-zone load balancing configuration
5. Auto Scaling groups and launch templates2 hrs
   • Auto Scaling policies: Target Tracking and Step Scaling
   • Launch template versioning and rollouts
   • Lifecycle hooks for graceful instance termination
   • Instance refresh strategies and warmup periods
   • Maintaining mixed instances policies across Spot and On-Demand
6. EC2 fleet troubleshooting and diagnostics90 min
   • System status checks vs instance status checks
   • Retrieving system logs and console screenshots
   • CloudWatch agent installation for memory metrics
   • Debugging user-data script failures via /var/log/cloud-init.log
   • Resolving volume attachment conflicts on boot

Hands-on project: Deploy an auto-scaling cluster of web servers behind an Application Load Balancer with custom health checks and instance refreshing.

You can configure durable object storage, lifecycle rules, and shared network file systems.

1. Amazon S3: buckets, objects and storage classes2 hrs
   • Bucket naming global uniqueness and region binding
   • S3 Standard, Standard-IA, One Zone-IA, and Glacier Instant Retrieval
   • Multipart uploads for files exceeding 100 MB
   • Object metadata, tags, and system attributes
   • S3 strong read-after-write consistency model
2. S3 security, versioning, lifecycle policies and replication2 hrs
   • S3 Block Public Access account and bucket settings
   • Lifecycle rule transitions and expiration actions
   • Cross-Region Replication (CRR) and Same-Region Replication (SRR)
   • Bucket policies enforcing secure transport (aws:SecureTransport)
   • Object versioning and MFA delete protection
3. Static website hosting on S390 min
   • Index document and error document configuration
   • Custom domain mapping with Route 53 aliases
   • Origin Access Control (OAC) for CloudFront integration
   • Redirect rules and CORS configuration
   • Hosting single-page applications on S3
4. Block and file storage with EBS and EFS90 min
   • EFS mount targets across multiple availability zones
   • EFS throughput modes: Bursting vs Provisioned
   • EFS lifecycle management and infrequent access transition
   • EBS volume resizing without downtime
   • Attaching EBS volumes across instances in the same AZ
5. Backups, Glacier and data transfer90 min
   • AWS Backup vaults, backup plans, and selection tags
   • Glacier Vault Lock compliance policies (WORM storage)
   • Snowball Edge device ordering and data migration
   • AWS DataSync configuration for on-premises NAS migration
   • Restoring point-in-time EBS snapshots
6. S3 performance optimization and analytics90 min
   • S3 Storage Lens dashboard configuration
   • Prefix performance optimization and parallel request scaling
   • S3 Select querying data with SQL statements
   • Access logs and S3 Inventory reporting
   • Troubleshooting 403 Access Denied errors on S3 objects

Hands-on project: Configure an S3 bucket with cross-region replication, bucket policies, and intelligent tiering alongside an attached EFS file share.

You can design isolated multi-tier cloud networks with custom routing, DNS, and content delivery.

1. VPC, subnets and CIDR blocks2 hrs
   • IPv4 CIDR notation and subnet mask calculations
   • Public vs private subnet architectural topologies
   • Default VPC vs custom VPC creation
   • Secondary CIDR block allocation
   • IPAM (IP Address Manager) overview
2. Route tables, Internet gateways and NAT gateways2 hrs
   • Route table creation and subnet association
   • Internet Gateway (IGW) attachment and 0.0.0.0/0 routing
   • NAT gateway high availability setup across AZs
   • Egress-only internet gateways for IPv6
   • VPC endpoints: Gateway endpoints vs Interface endpoints
3. Security groups vs network ACLs90 min
   • Stateful security group packet inspection mechanics
   • Stateless network ACL (NACL) rule evaluation and numbers
   • NACL ephemeral port range configuration for return traffic
   • Troubleshooting blocked traffic using VPC Flow Logs
   • Default NACL vs custom NACL best practices
4. Route 53 DNS and routing policies2 hrs
   • Public and private hosted zones configuration
   • Record types: A, AAAA, CNAME, TXT, and Alias records
   • Latency, weighted, and failover routing policies
   • Route 53 health checks and DNS failover triggers
   • Domain registration and delegation setup
5. CloudFront CDN and VPC peering2 hrs
   • CloudFront cache behaviors, TTL, and query string forwarding
   • Origin shielding and geographic restriction policies
   • VPC peering connection configuration and route propagation
   • Transit Gateway architecture for multi-VPC hubs
   • SSL certificate integration with CloudFront distributions
6. Advanced VPC troubleshooting and flow logs90 min
   • Enabling VPC Flow Logs to CloudWatch Logs or S3
   • Analyzing REJECT records for blocked packet flows
   • Resolving asymmetric routing issues across NAT gateways
   • Testing connectivity with Reachability Analyzer
   • Verifying DNS resolution inside private subnets

Hands-on project: Build a custom VPC with public and private subnets, NAT gateways, VPC peering, and a CloudFront distribution fronting an ALB.

You can deploy managed relational, NoSQL, and in-memory caching data layers with automated failover.

1. Amazon RDS and Aurora2 hrs
   • Multi-AZ deployment mechanics and synchronous replication
   • Automated backups and point-in-time recovery (PITR)
   • Aurora Serverless v2 capacity units (ACUs) scaling
   • RDS parameter groups and option groups management
   • Database subnet groups configuration
2. DynamoDB for NoSQL workloads2 hrs
   • Partition keys and sort keys design patterns
   • Provisioned vs On-Demand capacity billing modes
   • Global Secondary Indexes (GSIs) and Local Secondary Indexes (LSIs)
   • DynamoDB Streams and consumer triggering
   • Optimistic locking with version numbers
3. ElastiCache with Redis and Memcached90 min
   • Session caching and read-aside patterns
   • Redis cluster mode configuration and replication groups
   • Eviction policies (volatile-lru, allkeys-lru)
   • ElastiCache backup and restore workflows
   • Security groups and subnet groups for cache nodes
4. Backups, read replicas and database security90 min
   • RDS manual snapshot sharing across AWS accounts
   • IAM database authentication for PostgreSQL and MySQL
   • Encryption at rest using AWS KMS customer managed keys
   • Database auditing and logging exported to CloudWatch
   • Cross-region read replica promotion workflows
5. Choosing the right database for the job90 min
   • OLTP vs OLAP workload characteristics
   • Document, key-value, graph, and relational trade-offs
   • AWS Database Migration Service (DMS) for schema conversion
   • Amazon Redshift data warehousing architecture overview
   • DocumentDB compatibility with MongoDB
6. Database scaling and performance troubleshooting90 min
   • RDS Performance Insights and CPU utilization spikes
   • Identifying slow queries via CloudWatch logs
   • DynamoDB throttling errors (ProvisionedThroughputExceededException)
   • Connection pooling configuration with RDS Proxy
   • Resolving storage full alerts on RDS instances

Hands-on project: Deploy a multi-AZ Amazon RDS PostgreSQL instance with read replicas alongside a DynamoDB table with global secondary indexes.

You can build event-driven serverless APIs and workflows without provisioning servers.

1. Serverless concepts and AWS Lambda functions2 hrs
   • Lambda execution lifecycle and cold start mitigation
   • Memory allocation and CPU proportional scaling
   • Environment variables and Lambda layers for shared code
   • Lambda function URLs vs API Gateway integration
   • Provisioned concurrency configuration
2. Triggers and event sources90 min
   • S3 event notifications triggering Lambda functions
   • DynamoDB Streams integration with event source mappings
   • SQS queue batch size and polling configurations
   • Event filtering rules on event source mappings
   • Error handling and destination on failure configurations
3. Building REST APIs with API Gateway2 hrs
   • HTTP APIs vs REST APIs payload and latency differences
   • Request validation, authorizers, and mapping templates
   • API stages, deployment snapshots, and stage variables
   • Custom domain names and base path mapping
   • Throttling limits and burst rate control
4. Serverless data with DynamoDB and S390 min
   • Boto3 SDK integration in Lambda for DynamoDB CRUD
   • Handling payload size limits in Lambda and API Gateway
   • Generating presigned URLs for secure S3 direct client uploads
   • DynamoDB transactional writes across multiple items
   • Paginating query results in Lambda functions
5. Step Functions and event-driven architectures2 hrs
   • State machine definitions using Amazon States Language (ASL)
   • Express workflows vs Standard workflows execution models
   • EventBridge custom event buses and rule matching
   • Fan-out patterns with SNS topics triggering SQS queues
   • Error catchers and retry blocks in Step Functions
6. Serverless debugging, testing and X-Ray tracing90 min
   • AWS X-Ray service map and distributed tracing in Lambda
   • CloudWatch Lambda insights performance metrics
   • Local testing with AWS SAM CLI and sam local invoke
   • Debugging timeout errors and memory exhaustion
   • Structuring structured JSON logging in Lambda

Hands-on project: Build a serverless REST API using API Gateway, Lambda functions written in Python, and DynamoDB for persistent storage.

You can package, push, and orchestrate containerized applications using Amazon ECS and EKS.

1. Running containers on AWS90 min
   • Container orchestration fundamentals in cloud environments
   • EC2 launch type vs serverless Fargate execution model
   • Task definitions, CPU/memory allocations, and IAM task roles
   • Container health checks and restart policies
   • Logging configuration with awslogs driver
2. Elastic Container Registry (ECR)90 min
   • Docker credential helper authentication with aws ecr
   • Private repository creation and immutable image tags
   • Automated image vulnerability scanning with Trivy or Inspector
   • Lifecycle policies for automated tag pruning
   • Cross-account image sharing permissions
3. Amazon ECS and AWS Fargate2 hrs
   • ECS clusters, services, and task definitions
   • ALB target group integration with awsvpc network mode
   • ECS service auto-scaling based on CPU and memory utilization
   • Rolling update deployments and minimum healthy percent
   • Executing interactive shell commands with ECS Exec
4. Amazon EKS (managed Kubernetes)2 hrs
   • EKS control plane architecture and managed worker node groups
   • Configuring kubectl authentication with aws eks update-kubeconfig
   • IAM roles for service accounts (IRSA) configuration
   • EKS add-ons: VPC CNI, CoreDNS, and kube-proxy
   • Kubernetes secrets integration with AWS Secrets Manager
5. Deploying containerized applications90 min
   • Kubernetes deployment and service manifests on EKS
   • Cluster Autoscaler and Karpenter node provisioning
   • AWS Load Balancer Controller for Ingress resources
   • Persistent storage with EBS CSI driver on EKS
   • Troubleshooting PodCrashLoopBackOff errors on EKS
6. Container networking and security hardening90 min
   • Network policies in EKS with Calico or AWS VPC CNI
   • Running containers as non-root users in ECS/EKS
   • Scanning base images for CVEs prior to ECR push
   • Isolating multi-tenant workloads with namespaces
   • Debugging container networking with ephemeral debug containers

Hands-on project: Deploy a containerized microservice to Amazon ECS using Fargate, backed by an image stored in Amazon ECR.

You can set up centralized logging, metric alarms, encryption key management, and cost budgets.

1. CloudWatch metrics, logs, alarms and dashboards2 hrs
   • CloudWatch metric math and custom namespace publishing
   • CloudWatch Log groups, streams, and metric filters
   • Creating composite alarms and SNS notification endpoints
   • CloudWatch dashboards for multi-resource visualization
   • Contributor Insights for log analysis
2. CloudTrail and AWS Config90 min
   • Multi-region CloudTrail organizational trails
   • AWS Config managed compliance rules and remediation
   • Resource change history tracking and timeline inspection
   • Athena queries over CloudTrail S3 audit logs
   • GuardDuty threat detection integration
3. Encryption with KMS and Secrets Manager2 hrs
   • AWS Managed Keys vs Customer Managed Keys (CMKs)
   • KMS key policies, grants, and annual key rotation
   • Storing database credentials in AWS Secrets Manager
   • Automatic secret rotation with Lambda functions
   • Encrypting data across S3, EBS, and RDS
4. WAF, Shield and security best practices90 min
   • AWS WAF Web ACLs and managed rule groups (SQLi, XSS)
   • Rate-based rule limiting for DDoS mitigation
   • Shield Standard vs Shield Advanced protections
   • Associating WAF Web ACLs with ALBs and CloudFront
   • Logging WAF blocked requests to S3
5. Cost monitoring, budgets and optimization90 min
   • AWS Cost Anomaly Detection and SNS alerts
   • Reserved instances, Compute Savings Plans, and EC2 Instance Savings Plans
   • AWS Trusted Advisor cost-reduction recommendations
   • Identifying unattached EBS volumes and idle load balancers
   • Allocation tags and cost center reporting
6. Security auditing and compliance frameworks90 min
   • AWS Security Hub security score and standards
   • IAM Access Analyzer cross-account findings review
   • Penetration testing authorization and rules of engagement
   • Preparing evidence for SOC 2 and ISO 27001 audits
   • Remediating high-severity Inspector vulnerability alerts

Hands-on project: Configure CloudWatch custom dashboards and alarms, enable CloudTrail auditing, and set up encryption keys via KMS with automated budget alerts.

You can provision and manage cloud infrastructure repeatably using CloudFormation, Terraform, and CI/CD pipelines.

1. Infrastructure as Code with CloudFormation2 hrs
   • CloudFormation YAML template syntax and intrinsic functions
   • Stack sets, change sets, and rollback triggers
   • Nested stacks and cross-stack reference exports
   • CloudFormation drift detection
   • CDK (Cloud Development Kit) conceptual overview
2. Introduction to Terraform on AWS2 hrs
   • Terraform AWS provider configuration and version pinning
   • Remote state management with S3 backend and DynamoDB locking
   • Terraform modules, input variables, and output values
   • Resource dependency management and terraform plan/apply
   • Importing existing AWS resources into Terraform state
3. CI/CD with CodePipeline, CodeBuild and CodeDeploy2 hrs
   • buildspec.yml syntax and build lifecycle phases
   • Pipeline source, build, and deploy stage configuration
   • Blue/Green deployments with CodeDeploy and ECS/ASG
   • Integrating GitHub webhooks into CodePipeline
   • Manual approval stages in deployment pipelines
4. Messaging with SNS, SQS and EventBridge90 min
   • Pub/sub messaging patterns with SNS topics
   • SQS standard vs FIFO queues and message deduplication
   • Dead Letter Queues (DLQ) and redrive policies
   • EventBridge event bus routing rules and partner integrations
   • Decoupling microservices with asynchronous messaging
5. High availability and disaster recovery90 min
   • Backup and restore, pilot light, warm standby, and multi-region active-active
   • Recovery Point Objective (RPO) and Recovery Time Objective (RTO) calculations
   • Route 53 DNS failover configuration across regions
   • Cross-region RDS read replica promotion runbooks
   • Disaster recovery testing and chaos engineering principles
6. Terraform state management and advanced patterns90 min
   • Handling terraform state drift and workspace segregation
   • Refactoring infrastructure with terraform state mv
   • Writing reusable Terraform modules for VPC and RDS
   • Secrets management in Terraform using data sources
   • Automating terraform apply in CI/CD pipelines securely

Hands-on project: Build a complete three-tier infrastructure stack using Terraform and deploy application code via AWS CodePipeline.

You can clear AWS certification exams with structured test-taking strategies and targeted domain reviews.

1. AWS certification paths and how to choose90 min
   • Associate vs Professional certification tracks
   • Specialty exams: Security, Advanced Networking, Machine Learning
   • Prerequisite mapping and recertification requirements
   • Scheduling exams via Pearson VUE or online proctoring
   • Exam voucher management and preparation timeline
2. Cloud Practitioner and Solutions Architect Associate focus90 min
   • SAA-C03 exam blueprint breakdown and domain weights
   • Designing resilient architectures question patterns
   • High-performing storage solutions scenarios
   • Secure applications and architectures evaluation
   • Cost-optimized architectures evaluation
3. Exam structure, domains and question patterns2 hrs
   • Multiple choice vs multiple response tactics
   • Eliminating distractor answers in scenario questions
   • Time management strategies during the 130-minute exam
   • Marking questions for review and navigating question palettes
   • Understanding AWS phrasing for least privilege and high availability
4. Practice tests and exam strategy2 hrs
   • Simulated exam environment under timed conditions
   • Reviewing detailed answer explanation reports
   • Addressing weak knowledge areas identified in diagnostic tests
   • Analyzing common trap answers related to VPC endpoints and IAM
   • Final pre-exam checklist and ID verification guidelines
5. Hands-on review of frequently tested services90 min
   • S3 replication edge cases and versioning interactions
   • VPC endpoint types (Gateway vs Interface) exam scenarios
   • DynamoDB consistency models and throughput calculations
   • Aurora multi-master and global database failover mechanics
   • Direct Connect vs AWS Site-to-Site VPN selection criteria
6. Exam day readiness and final Q&A90 min
   • System test requirements for online proctored exams
   • ID document preparation and workspace clearance rules
   • Answering conceptual architecture troubleshooting questions
   • Managing exam anxiety and pacing during tough sections
   • Post-exam score report interpretation and digital badge claim

Hands-on project: Complete timed practice exams for the AWS Solutions Architect Associate certification, analyzing score reports and rectifying weak domains.

You can cut an AWS bill with evidence and review a workload against AWS's own framework.

1. Reading an AWS bill90 min
   • Cost Explorer and CUR
   • Tagging for allocation
   • Finding idle and orphaned resources
2. Paying less for the same thing90 min
   • Savings Plans vs Reserved
   • Spot for the right workloads
   • S3 storage classes
3. Right-sizing from evidence90 min
   • CloudWatch utilisation
   • Compute Optimizer
   • Scheduled shutdown
4. Well-Architected review90 min
   • The six pillars
   • Scoring a workload
   • Prioritising fixes

Hands-on project: Analyse a Cost Explorer export to find the three largest avoidable costs, implement budgets with alerts and a tagging policy, right-size from CloudWatch metrics, and deliver a Well-Architected review with ranked remediations.

You can design, build, test, and present an end-to-end production-grade cloud architecture on AWS.

1. Design a scalable, secure and cost-aware architecture2 hrs
   • Requirements gathering and topology drafting for capstone
   • Security boundary planning across public and private subnets
   • Cost estimation and optimization using AWS Pricing Calculator
   • Documenting architecture diagrams with C4 model or AWS icons
   • Defining RPO and RTO targets for the capstone system
2. Build it: VPC, compute, storage, database and security3 hrs
   • Writing modular Terraform code for the complete capstone stack
   • Provisioning custom VPC, subnets, IGW, and NAT gateways
   • Deploying multi-AZ RDS PostgreSQL and S3 encrypted buckets
   • Launching auto-scaling EC2 instances behind an ALB
   • Configuring least-privilege IAM roles and security groups
3. Add monitoring, auto scaling and infrastructure as code3 hrs
   • Configuring CloudWatch custom metric dashboards and alarms
   • Setting up Auto Scaling policies based on CPU and request count
   • Validating state consistency with terraform plan
   • Enabling AWS CloudTrail and VPC Flow Logs
   • Setting up SNS email alerts for infrastructure failures
4. Optimize for cost and document the design2 hrs
   • Implementing resource tagging strategies across all modules
   • Writing comprehensive architecture README and runbook documentation
   • Creating failure recovery procedures and rollback guides
   • Conducting peer architecture reviews and security audits
   • Tearing down test resources cleanly with terraform destroy
5. Portfolio, GitHub, mock interviews and career prep2 hrs
   • GitHub repository structuring for enterprise cloud projects
   • Resume refinement and cloud keyword optimization
   • Technical mock interview simulation for Cloud Engineer roles
   • Explaining architectural decisions during system design rounds
   • Navigating cloud architecture interview follow-up questions
6. Capstone project presentation and code review2 hrs
   • Live demonstration of deployed cloud infrastructure
   • Code review of Terraform modules with senior mentors
   • Validating security group rules and IAM policies
   • Demonstrating auto-scaling response under load testing
   • Receiving individualized feedback and certification roadmap advice

Hands-on project: Build and deploy a complete production web application architecture on AWS using Terraform, featuring a custom VPC, secure database, auto-scaling compute, CI/CD pipeline, and full CloudWatch monitoring.