EC2 — Virtual Servers

sequenceDiagram
    participant User as Developer
    participant Console as AWS Console/CLI
    participant EC2 as EC2 Service
    participant SG as Security Group
    participant Instance as EC2 Instance

    User->>Console: Launch instance<br/>(AMI, type, key pair)
    Console->>EC2: Create instance
    EC2->>SG: Attach security group
    EC2-->>Console: Instance running + IP

    Note over SG: Security Group Rules:
    Note over SG: Inbound: SSH (22), HTTP (80), HTTPS (443)
    Note over SG: Outbound: All traffic (default)

    User->>Instance: SSH (port 22)
    SG->>SG: Check: SSH inbound allowed?
    SG->>SG: Source IP in rules?
    alt Allowed
        SG-->>Instance: Allow connection ✅
    else Denied
        SG-->>User: Connection timed out ❌
    end

flowchart TB
    Question["What does your app need most?"] --> CPU{"CPU-heavy?<br/>Encoding, rendering<br/>batch processing"}
    Question --> Memory{"Memory-heavy?<br/>Caching, analytics<br/>in-memory DB"}
    Question --> Balanced{"Balanced?<br/>Web servers,<br/>microservices"}
    Question --> GPU{"GPU needed?<br/>ML, video transcoding<br/>3D rendering"}

    CPU -->|"c5/c6g series"| C_Family["c5.xlarge, c6g.2xlarge<br/>High CPU, reasonable RAM"]
    Memory -->|"r5/x1e series"| R_Family["r5.large, x1e.xlarge<br/>High RAM, moderate CPU"]
    Balanced -->|"m5/t3 series"| M_Family["m5.large, t3.medium<br/>Balanced CPU & RAM"]
    GPU -->|"g4dn/p3 series"| G_Family["g4dn.xlarge, p3.2xlarge<br/>NVIDIA GPU, ML-optimized"]

    style Question fill:#f59e0b,color:#fff
    style C_Family fill:#3b82f6,color:#fff
    style R_Family fill:#059669,color:#fff
    style M_Family fill:#7c3aed,color:#fff
    style G_Family fill:#ef4444,color:#fff

flowchart LR
    Pending["🟡 Pending<br/>Starting up"] --> Running["🟢 Running<br/>Billed for usage"]
    Running --> Stopping["🟡 Stopping"]
    Stopping --> Stopped["⏹️ Stopped<br/>Not billed for instance<br/>(EBS storage billed)"]
    Running --> Rebooting["🔄 Rebooting"]
    Rebooting --> Running
    Running --> Terminated["❌ Terminated<br/>Instance deleted<br/>Not recoverable"]
    Stopped --> Running
    Stopped --> Terminated

    style Running fill:#059669,color:#fff
    style Stopped fill:#f59e0b,color:#fff
    style Terminated fill:#ef4444,color:#fff

flowchart TB
    subgraph OnDemand["On-Demand — Pay as you go"]
        OD1["$$ per hour"]
        OD2["No commitment"]
        OD3["Good for dev/test"]
    end

    subgraph Reserved["Reserved — Commit for savings"]
        R1["$ per hour (up to 72% off)"]
        R2["1 or 3 year term"]
        R3["Best for steady production"]
    end

    subgraph Spot["Spot — Bid for spare"]
        S1["¢ per hour (up to 90% off)"]
        S2["Can be terminated at 2 min notice"]
        S3["Best for batch jobs, CI/CD"]
    end

    Cost{"More predictable load?"}
    Cost -->|"Yes — steady 24/7"| Reserved
    Cost -->|"No — spiky or new"| Interruptible{"Can tolerate<br/>interruptions?"}
    Interruptible -->|"Yes"| Spot
    Interruptible -->|"No"| OnDemand

    style OnDemand fill:#3b82f6,color:#fff
    style Reserved fill:#059669,color:#fff
    style Spot fill:#f59e0b,color:#fff