Business Platform

Internal documentation for the multi-tenant SaaS business management platform.

Live app: d2efo184qf3zrs.cloudfront.net
GitHub: mirrorhead-uk/supplier-platform
AWS account: 559401928829 · eu-west-1 (Ireland)

What is this?

Business Platform is a fully multi-tenant SaaS tool for small businesses. Each tenant gets a completely isolated workspace with their own data, users, and role-based access. It started as a supplier management tool and is expanding into a full business management suite.

Modules

Suppliers Live

Supply chain management with document uploads

Clients Live

Pipeline from lead to active with documents

People Live

HR records, salary, org chart, documents

Settings Live

Team management, roles, invitations

Contacts Live

Cross-entity contact records linked to suppliers and clients

Invoicing Planned

Client invoicing with PDF generation

Expenses Planned

Expense tracking with receipt uploads

Tech stack

Layer	Technology
Frontend	React 18, Vite, React Router, CSS Modules
Auth	AWS Cognito — User Pool + JWT
API	AWS API Gateway HTTP API
Compute	AWS Lambda Node.js 22.x (37 functions)
Database	DynamoDB single-table (`supplier-platform-v2`)
Storage	S3 — frontend bundle + document uploads
CDN	CloudFront with OAC + security headers

Architecture

All infrastructure lives in eu-west-1 (Ireland), AWS account 559401928829.

Request flow

Browser → CloudFront → S3          (React app — static files)
Browser → API Gateway → Lambda     (all REST endpoints)
Browser → Cognito                  (auth / JWT issuance)
Lambda  → DynamoDB                 (entity data)
Lambda  → S3                       (presigned document URLs)

AWS resources

Service	Resource ID	Purpose
CloudFront	`E1FIHLCB86M2CF`	CDN, security headers, OAC
S3 frontend	`supplier-platform-frontend-559401928829`	React bundle (private)
API Gateway	`ycn03ustd3`	HTTP API — all endpoints
Lambda	32 functions	All business logic
DynamoDB	`supplier-platform-v2`	All entity data
S3 documents	`supplier-platform-documents-559401928829`	File uploads
Cognito	`eu-west-1_hGgmpHBHQ`	Auth, user pools, groups
IAM	`supplier-platform-lambda-role`	Lambda execution role

Multi-tenancy

Tenant isolation is enforced at three independent layers:

Cognito — users belong to a group named tenant-{id}. The tenantId is embedded in the JWT as custom:tenantId.
Lambda — shared/auth.js extracts tenantId from the JWT on every request. No request can claim another tenant's ID.
DynamoDB — every record has tenantId as its partition key. All queries are scoped to tenantId = :tid. Cross-tenant reads are structurally impossible.

Tenant roles

Cognito group	Access level
`tenant-id:admin`	Full access — manage team and all data
`tenant-id:contributor`	Create and edit records
`tenant-id:readonly`	View only
`platform-admin`	Platform back-office — all tenants

Database — single-table design

Table: supplier-platform-v2 · PK: tenantId · SK: entityType#entityId

Entity	SK prefix	Example
Supplier	`SUPPLIER#`	`SUPPLIER#sup-abc123`
Client	`CLIENT#`	`CLIENT#cli-xyz789`
Employee	`EMPLOYEE#`	`EMPLOYEE#emp-def456`
Contact	`CONTACT#`	`CONTACT#con-mno789`
Invoice	`INVOICE#`	`INVOICE#inv-ghi012` (planned)
Expense	`EXPENSE#`	`EXPENSE#exp-jkl345` (planned)

Note: sk is a DynamoDB reserved word. Always alias it as #sk using ExpressionAttributeNames: { '#sk': 'sk' } in any expression.

Security: Deletion protection ON · PITR (point-in-time recovery) ON · AES-256 encryption

Document storage

S3 path structure:

s3://supplier-platform-documents-559401928829/
  {tenantId}/{entityId}/{category}/{fileId}__{fileName}

Upload flow: Frontend calls Lambda to get a presigned PUT URL (5 min TTL) → browser uploads directly to S3 → Lambda never touches file bytes. Download links are presigned GET URLs with 1-hour TTL, generated at list time.

Modules

Feature documentation for each module in the platform.

Suppliers Live

Routes: /suppliers, /suppliers/:id

Manage the company's supply chain. Each supplier record tracks contact info, category, relationship owner, goods supplied, and status.

Statuses

Status	Meaning
Active	Current, trusted supplier
Pending	Under review / onboarding
Inactive	No longer used
Rejected	Failed vetting

Documents

Five categories: Certifications, Contracts & Agreements, Quotes, Invoices, Other. Drag-and-drop upload directly to S3 via presigned URL.

Clients Live

Routes: /clients, /clients/:id

Manage client relationships with a sales pipeline model. Notes are inline-editable (click to edit, ⌘↵ to save).

Pipeline

Lead → Prospect → Proposal → Active → Inactive

Documents

Three categories: Contracts & Agreements, Quotes, Invoices.

People (HR) Live

Routes: /people, /people/:id

Employee records. Separate from platform users — an employee does not need a platform login. Optionally linked to a Cognito user via userId.

Key fields

firstName, lastName, fullName, jobTitle, department, employmentType, status, startDate, workEmail, personalEmail, phone, salary (annual GBP), managerId (links to another employee), userId (optional Cognito link), notes

Statuses

Status	Meaning
Active	Currently employed
On leave	Temporarily absent
Terminated	No longer employed

Documents

Four categories: Contracts, Right to Work, Qualifications, Other Docs.

Contacts Live

Route: /contacts, /contacts/:id

A cross-entity contact book. Each contact record represents a named person or company and can be linked to any number of suppliers and/or clients. Contacts are created automatically when a supplier or client is added (using the entity name as the contact name and the "Contact details" field as free-text contact info), and can also be created manually from the Contacts page.

Key fields

name (required), contactDetails (free-text — email, phone, address, etc.), linkedSuppliers[] (supplier IDs), linkedClients[] (client IDs), isPrimary (boolean — marks the primary contact for a supplier or client), notes, sourceType (manual | supplier | client), sourceId

Primary contacts

Each supplier and client detail page shows a "Primary contact" section (the contact with isPrimary: true linked to that entity) and an "Additional contacts" section for all others. The primary contact can be changed from the supplier or client detail page — the change is applied optimistically in the UI and two PATCH calls are fired in sequence to promote the new primary and demote the old one.

Linking

Linked suppliers and clients are shown in the contact detail modal and are clickable — they navigate directly to the supplier or client detail page. Additional supplier and client links can be added inline from the contact modal using the link picker.

Settings Live

Route: /settings (tenant admins only)

Role	Permissions
Admin	Full access — manage team and all data
Contributor	Create and edit records
Read only	View only

Admin back-office Live

Route: /admin (platform-admin group only)

Separate area with distinct dark sidebar. Inaccessible to tenant users. Manage all tenants — create, list, and permanently delete tenants with all their data.

API Reference

Base URL: https://ycn03ustd3.execute-api.eu-west-1.amazonaws.com
All endpoints require Authorization: Bearer <cognito-id-token>. The tenant is derived from the JWT.

Suppliers

Method	Path	Lambda	Description
`GET`	`/suppliers`	`listSuppliers`	List all suppliers
`POST`	`/suppliers`	`createSupplier`	Create a supplier
`GET`	`/suppliers/{id}`	`getSupplier`	Get one supplier
`PUT`	`/suppliers/{id}`	`updateSupplier`	Update supplier
`DELETE`	`/suppliers/{id}`	`deleteSupplier`	Delete supplier
`GET`	`/suppliers/{id}/documents`	`listDocuments`	List documents grouped by category
`POST`	`/suppliers/{id}/documents/upload-url`	`getUploadUrl`	Get presigned S3 upload URL
`DELETE`	`/suppliers/{id}/documents`	`deleteDocument`	Delete a document (body: `{ s3Key }`)

Clients

Method	Path	Lambda	Description
`GET`	`/clients`	`listClients`	List all clients
`POST`	`/clients`	`createClient`	Create a client
`GET`	`/clients/{id}`	`getClient`	Get one client
`PUT`	`/clients/{id}`	`updateClient`	Update client
`DELETE`	`/clients/{id}`	`deleteClient`	Delete client
`GET`	`/clients/{id}/documents`	`listClientDocuments`	List documents grouped by category
`POST`	`/clients/{id}/documents/upload-url`	`getClientUploadUrl`	Get presigned S3 upload URL
`DELETE`	`/clients/{id}/documents`	`deleteClientDocument`	Delete a document

Employees

Method	Path	Lambda	Description
`GET`	`/employees`	`listEmployees`	List all employees
`POST`	`/employees`	`createEmployee`	Create an employee
`GET`	`/employees/{id}`	`getEmployee`	Get one employee
`PUT`	`/employees/{id}`	`updateEmployee`	Update employee
`DELETE`	`/employees/{id}`	`deleteEmployee`	Delete employee
`GET`	`/employees/{id}/documents`	`listEmployeeDocuments`	List documents grouped by category
`POST`	`/employees/{id}/documents/upload-url`	`getEmployeeUploadUrl`	Get presigned S3 upload URL
`DELETE`	`/employees/{id}/documents`	`deleteEmployeeDocument`	Delete a document

Contacts

Method	Path	Lambda	Description
`GET`	`/contacts`	`listContacts`	List all contacts
`POST`	`/contacts`	`createContact`	Create a contact
`GET`	`/contacts/{id}`	`getContact`	Get one contact
`PUT`	`/contacts/{id}`	`updateContact`	Update contact fields
`DELETE`	`/contacts/{id}`	`deleteContact`	Delete a contact

Team management

Method	Path	Description
`GET`	`/team`	List all users in the tenant
`POST`	`/team/invite`	Invite a new user
`PUT`	`/team/{username}/role`	Change a user's role
`DELETE`	`/team/{username}`	Remove a user (must be suspended first)
`POST`	`/team/{username}/suspend`	Suspend a user
`POST`	`/team/{username}/unsuspend`	Unsuspend a user

Admin (platform-admin only)

Method	Path	Description
`GET`	`/admin/tenants`	List all tenants on the platform
`POST`	`/admin/tenants`	Create a new tenant + first admin user
`DELETE`	`/admin/tenants/{tenantId}`	Delete a tenant and all its data

Document upload pattern

All upload-url endpoints accept the same request body:

{
  "fileName": "contract.pdf",
  "fileType": "application/pdf",
  "fileSize": 102400,
  "category": "contracts"
}

Returns a presigned S3 URL. The browser then PUTs the file directly to S3 — Lambda never handles file bytes. Download URLs in list responses are presigned GET URLs with a 1-hour TTL.

Lambda functions

All 37 Lambda functions. Runtime: nodejs22.x. All share a single deployment bundle at backend/functions.zip. Shared helpers live in backend/functions/shared/.

Shared helpers: shared/auth.js — extracts JWT claims, checks roles · shared/db.js — DynamoDB client + key helpers (sk(), skPrefix(), idFromSk()) · shared/response.js — ok() / error() builders, getTenantId() · shared/roles.js — role constants

Suppliers — 8 functions

listSuppliers GET /suppliers

Returns all supplier records for the authenticated tenant.

Queries DynamoDB with begins_with(#sk, 'SUPPLIER#') to return only supplier entities from the single-table design, excluding any other entity types that share the partition key.

DynamoDB QueryTenant-scoped

getSupplier GET /suppliers/{id}

Fetches a single supplier record by its ID.

Performs a DynamoDB GetItem using the composite key tenantId + SUPPLIER#{id}. Returns 404 if not found.

DynamoDB GetItem

createSupplier POST /suppliers

Creates a new supplier record for the tenant.

Validates required fields (name, category, relationshipOwner, goods). Accepts optional contactDetails (free-text contact info). Generates a sup-{uuid} ID and writes to DynamoDB with attribute_not_exists(#sk). If contactDetails is provided, the frontend fires a best-effort POST /contacts to create a linked primary contact using the supplier name and contact details — this is handled client-side after the supplier is created.

DynamoDB PutItemValidation

updateSupplier PUT /suppliers/{id}

Updates allowed fields on an existing supplier record.

Fetches the existing record first to verify ownership, then performs a UpdateItem on only the fields present in the request body. Always updates updatedAt. Returns the full updated record via ReturnValues: ALL_NEW.

DynamoDB UpdateItemOwnership check

deleteSupplier DELETE /suppliers/{id}

Permanently deletes a supplier record.

Fetches the record first to verify it exists and belongs to the tenant before deleting. Does not delete associated S3 documents — those are managed separately.

DynamoDB DeleteItemOwnership check

getUploadUrl POST /suppliers/{id}/documents/upload-url

Generates a presigned S3 PUT URL so the browser can upload a document directly to S3.

Validates the category (certifications, contracts, quotes, invoices, other) and enforces a 50MB file size limit. Stores the file at {tenantId}/{supplierId}/{category}/{uuid}__{fileName}. URL expires in 5 minutes. Lambda never handles file bytes.

S3 presigned URL50MB limit

listDocuments GET /suppliers/{id}/documents

Lists all documents for a supplier, grouped by category with presigned download URLs.

Uses ListObjectsV2 on the S3 prefix {tenantId}/{supplierId}/, then generates a presigned GET URL (1-hour TTL) for each object. Groups results into the five document categories and returns the full grouped structure.

S3 ListObjectsPresigned download URLs

deleteDocument DELETE /suppliers/{id}/documents

Deletes a document from S3. Requires tenant-admin role.

Accepts s3Key in the request body. Validates that the key starts with {tenantId}/{supplierId}/ before deleting — prevents cross-tenant or cross-supplier deletion even if a malicious key is supplied.

S3 DeleteObjectAdmin onlyKey validation

Clients — 8 functions

listClients GET /clients

Returns all client records for the authenticated tenant.

Queries DynamoDB with begins_with(#sk, 'CLIENT#') to return only client entities.

DynamoDB QueryTenant-scoped

getClient GET /clients/{id}

Fetches a single client record by ID.

GetItem using tenantId + CLIENT#{id}. Returns 404 if not found.

DynamoDB GetItem

createClient POST /clients

Creates a new client record for the tenant.

Required fields: name, relationshipOwner. Default status is lead. Generates a cli-{uuid} ID. Validates status against the pipeline values: lead, prospect, proposal, active, inactive.

DynamoDB PutItemPipeline status

updateClient PUT /clients/{id}

Updates allowed fields on an existing client record.

Allowed fields: name, contactDetails, website, status, relationshipOwner, industry, notes. Verifies ownership before updating. Used by the Edit drawer and the inline notes editor on the client detail page. After a successful edit, the frontend also patches contactDetails on the primary linked contact via PUT /contacts/{id}.

DynamoDB UpdateItemPartial update

deleteClient DELETE /clients/{id}

Permanently deletes a client record.

Verifies the record exists and belongs to the tenant before deleting. Does not cascade-delete S3 documents.

DynamoDB DeleteItemOwnership check

getClientUploadUrl POST /clients/{id}/documents/upload-url

Generates a presigned S3 PUT URL for uploading a client document.

Valid categories: contracts, quotes, invoices. 50MB limit. Path: {tenantId}/{clientId}/{category}/{uuid}__{fileName}.

S3 presigned URL50MB limit

listClientDocuments GET /clients/{id}/documents

Lists all documents for a client, grouped by category with presigned download URLs.

Same pattern as listDocuments — lists S3 objects under the client prefix, generates presigned GET URLs (1-hour TTL), groups by the three client categories.

S3 ListObjectsPresigned download URLs

deleteClientDocument DELETE /clients/{id}/documents

Deletes a client document from S3. Requires tenant-admin role.

Validates the s3Key starts with {tenantId}/{clientId}/ before deleting.

S3 DeleteObjectAdmin onlyKey validation

Employees — 8 functions

listEmployees GET /employees

Returns all employee records for the authenticated tenant.

Queries DynamoDB with begins_with(#sk, 'EMPLOYEE#'). Used by the People list page and also loaded by the employee detail page to populate the line-manager search dropdown.

DynamoDB QueryTenant-scoped

getEmployee GET /employees/{id}

Fetches a single employee record by ID.

GetItem using tenantId + EMPLOYEE#{id}. Returns 404 if not found.

DynamoDB GetItem

createEmployee POST /employees

Creates a new employee HR record for the tenant.

Required fields: firstName, lastName. Generates fullName automatically. Generates an emp-{uuid} ID. Key fields: jobTitle, department, employmentType (full-time/part-time/contractor/intern), status (active/on-leave/terminated), startDate, workEmail, personalEmail, phone, salary (number, annual GBP), managerId (optional — another employeeId), userId (optional — a Cognito username to link the HR record to a platform login).

DynamoDB PutItemfullName computed

updateEmployee PUT /employees/{id}

Updates allowed fields on an existing employee record.

Automatically recomputes fullName if firstName or lastName changes. Validates salary is a number. Used by the Edit drawer, the inline notes editor, and the inline line-manager picker on the employee detail page — all three call this same endpoint with different subsets of fields.

DynamoDB UpdateItemfullName syncPartial update

deleteEmployee DELETE /employees/{id}

Permanently deletes an employee HR record.

Verifies ownership before deleting. Does not cascade-delete S3 documents or unlink the managerId on other employees who report to this person.

DynamoDB DeleteItemOwnership check

getEmployeeUploadUrl POST /employees/{id}/documents/upload-url

Generates a presigned S3 PUT URL for uploading an employee document.

Valid categories: contracts, right-to-work, qualifications, other. 50MB limit. Path: {tenantId}/{employeeId}/{category}/{uuid}__{fileName}.

S3 presigned URL50MB limit

listEmployeeDocuments GET /employees/{id}/documents

Lists all documents for an employee, grouped by category with presigned download URLs.

Lists S3 objects under the employee prefix, generates presigned GET URLs (1-hour TTL), and groups into four HR-specific categories.

S3 ListObjectsPresigned download URLs

deleteEmployeeDocument DELETE /employees/{id}/documents

Deletes an employee document from S3. Requires tenant-admin role.

Validates the s3Key starts with {tenantId}/{employeeId}/ before deleting.

S3 DeleteObjectAdmin onlyKey validation

Team management — 5 functions

tenantListUsers GET /team

Lists all users in the current tenant's Cognito group, with their roles and account status.

Queries ListUsersInGroup on the tenant's Cognito group, then calls AdminListGroupsForUser for each user to determine their role sub-group (:admin, :contributor, :readonly). Returns enriched user objects including email, role label, account status, and createdAt.

CognitoRole resolution

tenantInviteUser POST /team/invite

Invites a new user to the tenant by creating a Cognito account and assigning them a role.

Calls AdminCreateUser which triggers Cognito to send an invitation email with a temporary password. Adds the user to the tenant group and the appropriate role sub-group. Only tenant admins can invite users.

CognitoSends invite emailAdmin only

tenantUpdateUserRole PUT /team/{username}/role

Changes a team member's role within the tenant.

Removes the user from all existing role sub-groups (:admin, :contributor, :readonly) then adds them to the new role group. Prevents admins from changing their own role. Only tenant admins can change roles.

CognitoAdmin only

tenantSuspendUser POST /team/{username}/suspend · /team/{username}/unsuspend

Suspends or unsuspends a team member. One function handles both actions.

Suspended users cannot log in but their account and all associated data are preserved. Uses AdminDisableUser / AdminEnableUser in Cognito. The action is determined from the URL path. Only tenant admins can suspend users. A user must be suspended before they can be permanently deleted.

CognitoAdmin onlyDual-action

tenantRemoveUser DELETE /team/{username}

Permanently deletes a user from the tenant. The user must be suspended first.

Calls AdminDeleteUser in Cognito. Enforces the suspension prerequisite as a safety guard against accidental deletion of active accounts. Only tenant admins can delete users. This action cannot be undone.

CognitoAdmin onlyRequires suspension first

Contacts — 5 functions

listContacts GET /contacts

Returns all contact records for the authenticated tenant.

Queries DynamoDB with begins_with(#sk, 'CONTACT#'). Each record includes linkedSuppliers[] and linkedClients[] arrays so the frontend can resolve linked entity names without additional requests.

DynamoDB QueryTenant-scoped

getContact GET /contacts/{id}

Fetches a single contact record by ID.

GetItem using tenantId + CONTACT#{id}. Returns 404 if not found.

DynamoDB GetItem

createContact POST /contacts

Creates a new contact record for the tenant.

Required: name. Optional: contactDetails (free-text — email, phone, address, etc.), linkedSuppliers[], linkedClients[], isPrimary (boolean), notes, sourceType (manual | supplier | client), sourceId. Generates a con-{uuid} ID. Contacts created automatically on supplier/client creation use sourceType: 'supplier' or 'client' and set isPrimary: true.

DynamoDB PutItemValidation

updateContact PUT /contacts/{id}

Updates allowed fields on an existing contact record.

Allowed fields: name, contactDetails, linkedSuppliers, linkedClients, isPrimary, notes. Verifies ownership before updating. Used by the contact detail modal (notes editing, link picker), the EditSupplier/EditClient drawers (syncing contactDetails on the primary contact), and the "Make primary" button on supplier/client detail pages (promotes/demotes isPrimary).

DynamoDB UpdateItemPartial update

deleteContact DELETE /contacts/{id}

Permanently deletes a contact record.

Verifies the record exists and belongs to the tenant before deleting. Does not cascade-update linkedSuppliers or linkedClients on the deleted contact's linked entities.

DynamoDB DeleteItemOwnership check

Platform admin — 3 functions (platform-admin group only)

adminListTenants GET /admin/tenants

Lists all tenants on the platform with user counts and creation dates.

Calls ListGroups on the Cognito User Pool and filters to top-level tenant groups — those starting with tenant- and containing no colon (which would indicate a role sub-group like tenant-id:admin). For each tenant, calls ListUsersInGroup to get the user count. Uses the group Description field as the display name (set by adminCreateTenant), falling back to deriving a name from the group name if the description is the legacy format.

CognitoPlatform-admin only

adminCreateTenant POST /admin/tenants

Creates a new tenant workspace and its first admin user.

Takes companyName and adminEmail. Generates a URL-safe tenantId from the company name (e.g. tenant-acme-ltd). Creates a Cognito group for the tenant with the company name stored in the Description field. Creates the first user via AdminCreateUser — Cognito sends an invitation email with a temporary password. Adds the user to the tenant group. Sets custom:tenantId and custom:tenantName as Cognito user attributes.

CognitoPlatform-admin onlySends invite email

adminDeleteTenant DELETE /admin/tenants/{tenantId}

Permanently and irreversibly deletes a tenant and all of its data.

Requires the confirmTenantId field in the request body to match the path parameter — a safety check to prevent accidental deletion. Performs three sequential operations: (1) deletes all Cognito users in the tenant group, (2) deletes the tenant group and all role sub-groups (:admin, :contributor, :readonly), (3) scans and deletes all DynamoDB records where tenantId matches — this covers all entity types (suppliers, clients, employees, etc.). Guards against deleting platform-admin or role sub-groups directly.

CognitoDynamoDBPlatform-admin onlyIrreversible

Deployment

How to build and deploy the frontend and backend.

SSO note: AWS SSO sessions expire periodically. If you see UnrecognizedClientException, run aws sso login --profile mirrorhead-dev first.

Frontend deploy

cd /path/to/Supplier-Platform
./scripts/deploy.sh

Builds with Vite → syncs hashed assets to S3 with Cache-Control: immutable → syncs index.html with no-cache → invalidates CloudFront /*.

Backend deploy

./backend/scripts/deploy.sh

Bundles all backend/functions/ into a single zip, then for each Lambda: updates code → waits → updates runtime to nodejs22.x → waits. Takes ~10 minutes. The waits are necessary — Lambda blocks config changes while a code update propagates.

Adding a new Lambda

Write the handler in backend/functions/yourFunction.js
Add to the FUNCTIONS array in backend/scripts/deploy.sh
Copy an existing setup script (e.g. setup-clients-api.sh) and adapt it
Run the setup script once to create the Lambda and API Gateway route
Future deploys via deploy.sh will keep it updated

Environment variables

Frontend (`.env`)

Variable	Value
`VITE_API_BASE_URL`	`https://ycn03ustd3.execute-api.eu-west-1.amazonaws.com`
`VITE_DEV_TENANT_ID`	`tenant-dev-001`
`VITE_COGNITO_REGION`	`eu-west-1`
`VITE_COGNITO_USER_POOL_ID`	`eu-west-1_hGgmpHBHQ`
`VITE_COGNITO_CLIENT_ID`	`7ecs96dmcldrq7856jk67rs0l7`

Lambda env vars (per function)

Variable	Value
`TABLE_NAME`	`supplier-platform-v2`
`USER_POOL_ID`	`eu-west-1_hGgmpHBHQ`
`DOCUMENTS_BUCKET`	`supplier-platform-documents-559401928829`
`CORS_ORIGIN`	`https://d2efo184qf3zrs.cloudfront.net`

Updating these docs

Edit docs/index.html in the repo and push. Cloudflare Pages rebuilds within ~30 seconds — no build step required.

Decision Log

Key architectural decisions, why we made them, and the trade-offs involved.

Single-table DynamoDB design

All entity types live in one table: tenantId (PK) + entityType#entityId (SK).

Why: DynamoDB performs best with access patterns baked into the key structure. One table means one IAM policy, one set of backups, one billing unit. Adding a new entity type is zero-infrastructure — just a new SK prefix.

Trade-offs: Harder to reason about for newcomers. sk is a DynamoDB reserved word — requires ExpressionAttributeNames: { '#sk': 'sk' } in all expressions.

Serverless compute (Lambda only)

Why: Zero infrastructure management. Pay-per-request — effectively free for the first 1M requests/month. Cold starts (~200ms) acceptable for B2B use.

Trade-offs: All functions share one bundle — a bad require() breaks everything. 15-minute execution limit (not a current constraint).

Cognito for auth

Why: Native AWS integration, free up to 10,000 MAU, handles email verification and password reset. Groups map cleanly to tenant roles.

Trade-offs: Single-region only — no native multi-region HA. JWT validation is trust-based (claims read without signature verification) — sufficient for internal use.

Presigned S3 URLs for document upload

Why: Browser uploads directly to S3. Lambda never handles file bytes — no 6MB payload limit, no base64 overhead, no bandwidth costs through Lambda.

Trade-offs: Two round trips instead of one. Download links expire after 1 hour.

Bash scripts instead of Terraform/CDK

Why: Speed of iteration — a new Lambda + route is ~20 lines of bash. No state file drift. Fully transparent.

Trade-offs: Setup scripts are not idempotent. No drift detection.

Mitigation: Named setup-*.sh (run once) vs deploy.sh (idempotent, run every deploy).

eu-west-1 (Ireland) as primary region

Why: Closest AWS region to UK/Europe. GDPR-compliant EU data residency. Full service availability.

Future HA region: eu-central-1 (Frankfurt) — nearest alternative EU region with full service parity.

Business Platform

What is this?

Modules

Tech stack

Architecture

Request flow

AWS resources

Multi-tenancy

Tenant roles

Database — single-table design

Document storage

Modules

Suppliers Live

Statuses

Documents

Clients Live

Pipeline

Documents

People (HR) Live

Key fields

Statuses

Documents

Contacts Live

Key fields

Primary contacts

Linking

Settings Live

Admin back-office Live

API Reference

Suppliers

Clients

Employees

Contacts

Team management

Admin (platform-admin only)

Document upload pattern

Lambda functions

Deployment

Frontend deploy

Backend deploy

Adding a new Lambda

Environment variables

Frontend (.env)

Lambda env vars (per function)

Updating these docs

Decision Log

Single-table DynamoDB design

Serverless compute (Lambda only)

Cognito for auth

Presigned S3 URLs for document upload

Bash scripts instead of Terraform/CDK

eu-west-1 (Ireland) as primary region

Frontend (`.env`)