S3 presigned URL upload sequence diagram template

Participants in this sequence diagram

• Browser
• Backend API
• S3 bucket
• Lambda processor
• Database

How to use this sequence diagram template

1. Click Open in the editor. The sequence diagram opens on a new page in FlowDiagram — nothing is uploaded and there is no sign-up.
2. Rename, add or delete shapes and drag them where you want; connectors stay attached as things move.
3. Drop in vendor logos from the library — 1,160 of them, including every AWS, Azure and Google Cloud service icon — or restyle it with the colour and theme controls.
4. Prefer text? Edit the Mermaid source below and paste it in through ☰ → Import diagram (see the Mermaid editor); it imports as an editable diagram.
5. Export to PNG, SVG or PDF, or press Ctrl+L for a link that carries the whole diagram.

Mermaid source

The whole template is the text below. Paste it into FlowDiagram, keep it in Git next to the code it describes, or hand it to an AI assistant to extend.

sequenceDiagram
  autonumber
  actor U as Browser
  participant API as Backend API
  participant S3 as S3 bucket
  participant Fn as Lambda processor
  participant DB as Database
  U->>API: POST /uploads {name, size, type}
  API->>API: Check auth, quota and MIME type
  alt Allowed
    API->>DB: Insert upload row (pending)
    API-->>U: Presigned PUT URL (expires 15 min)
    U->>S3: PUT file bytes to presigned URL
    S3-->>U: 200 ETag
    S3->>Fn: ObjectCreated event
    Fn->>Fn: Virus scan and thumbnail
    Fn->>DB: Mark upload ready
    U->>API: GET /uploads/123
    API-->>U: status ready + download URL
  else Rejected
    API-->>U: 413 or 415 error
  end
  Note over U,S3: File bytes never pass through the API servers

Related: Mermaid editor · All uml: sequence, class & state templates · All 521 templates