azuresql-db-local-to-cloud

---
name: azuresql-db-local-to-cloud
description: >-
license: MIT
---

# From the Azure SQL Database container to Azure SQL Database: same code, local to cloud

Build and test against the local container, then deploy the
**same application code** to Azure SQL Database in the cloud. Only the
connection string changes. Nothing else.

This works because the local container is the **Azure SQL Database engine**, not
the SQL Server image. `SELECT SERVERPROPERTY('EngineEdition')` returns `5`
and `SERVERPROPERTY('Edition')` returns `'SQL Azure'`, the same as the cloud. So
the SQL surface your code depends on is the same in both places.

## The one rule

**Do not change application code between local and cloud.** The application reads
its connection string from a single environment variable, `SQL_CONNECTION_STRING`.
Local development sets it to the container; cloud deployment sets it to the Azure
SQL server. Same binaries, same queries, same schema.

If you find yourself editing queries, drivers, or schema to "make it work in
Azure", stop: that is a bug. The only thing that legitimately differs is the
connection string (and, with it, the auth method).

## The single env var, two values

Standardize on `SQL_CONNECTION_STRING`. Use `User Id=` / `Password=` /
`Database=` (never `Uid=` / `Pwd=`).

Local (container, SA auth):

```
Server=localhost,1433;Database=appdb;User Id=sa;Password=YourStr0ng_Passw0rd;TrustServerCertificate=true
```

Cloud (Azure SQL Database, Microsoft Entra auth):

```
Server=your-server.database.windows.net,1433;Database=appdb;Authentication=Active Directory Default;Encrypt=true
```

Note what stays identical: `Database=appdb`, the table names, the parameterized
SQL. Only `Server`, the auth fields, and TLS posture move.

## Local SA auth vs cloud Entra auth (why, not just how)

Local: the container is provisioned with one bootstrap login, `sa`, set via the
`MSSQL_SA_PASSWORD` environment variable. There is no identity provider required
in front of a container on your laptop, so password auth over a trusted
self-signed cert (`TrustServerCertificate=true`) is the pragmatic local default.

Microsoft Entra ID authentication **does** work on the container (configure with
the `MSSQL_AAD_*` variables and a certificate mount; see the
`azuresql-db-container` skill, `references/entra-auth.md`). Use it when you
want closer local-to-cloud parity. Most local-to-cloud flows still start with SQL
auth locally and switch only the connection string for Entra in the cloud.

Cloud: Azure SQL Database sits behind Microsoft Entra ID. Instead of shipping a
password, the app presents a token from its Entra identity (a managed identity
in production, your developer sign-in locally against the cloud). The driver
acquires the token; you never put a secret in the connection string. TLS is
real and enforced, so use `Encrypt=true` and drop `TrustServerCertificate`.

The application code does not branch on this. The driver reads the
`Authentication=` keyword (or its absence) from the connection string and does
the right thing. That is the whole point: auth is configuration, not code.

Full walkthrough, token flow, and per-stack auth setup: see
[references/auth-local-vs-cloud.md](references/auth-local-vs-cloud.md).

## Minimal load-bearing facts about the local container

Just enough to run the examples on a fresh container. For full detail see the
**azuresql-db-container** skill.

- Image: `sqldbpreview-dpgaeqhmgphzd4bk.azurecr.io/azure-sql/db-dev:latest`
  (x64, `linux/amd64`). Private preview registry: run
  `docker login sqldbpreview-dpgaeqhmgphzd4bk.azurecr.io` first using the shared
  pull-only credentials provided to the Private Preview cohort (get them by signing up at https://aka.ms/sqldbcontainerpreview-signup; they may rotate). Registry and tag are
  provisional during Private Preview.
- On a non-x64 host, add `--platform linux/amd64`.
- Required env: `ACCEPT_EULA=Y` and a complex `MSSQL_SA_PASSWORD`
  (8+ chars, upper/lower/digit/symbol). Engine listens on 1433.
- **The engine does not auto-create databases.** You must
  `CREATE DATABASE appdb` on a **master** connection before connecting with
  `Database=appdb`. The `master` connection is for provisioning only; do real
  work on `appdb`.
- Avoid `USE` to switch databases. In a user-database session (the
  Azure-faithful context where you develop), `USE` returns `Msg 40508`, exactly
  as in Azure SQL Database in the cloud. A `master` connection is a provisioning
  provisioning session where the Azure statement filter is not enforced, so `USE` appears to work there, but `master` is for provisioning
  only, not application work. Always select the target database in the connection
  string (`Database=appdb`, or `-d appdb` for sqlcmd).

## Start the container and provision appdb (canonical recipe)

Run this once. It picks a free host port, adds `--platform` only when needed,
waits for real readiness, and provisions `appdb` inside the retry loop. The
`-b -l 2` makes a transient startup error (for example `Msg 913`) set the exit
code so the loop retries instead of masking it.

```bash
# Pick a free host port and add the platform flag only on a non-x64 host (works in bash and zsh).
HOST_PORT=1433; while lsof -nP -iTCP:"$HOST_PORT" -sTCP:LISTEN >/dev/null 2>&1; do HOST_PORT=$((HOST_PORT+1)); done
PLATFORM=(); case "$(docker info -f '{{.Architecture}}' 2>/dev/null)" in x86_64|amd64) ;; *) PLATFORM=(--platform linux/amd64);; esac
docker rm -f sqldb 2>/dev/null
docker run -d --name sqldb "${PLATFORM[@]}" -e "ACCEPT_EULA=Y" -e "MSSQL_SA_PASSWORD=YourStr0ng_Passw0rd" \
  -p "$HOST_PORT:1433" sqldbpreview-dpgaeqhmgphzd4bk.azurecr.io/azure-sql/db-dev:latest
until docker exec sqldb /opt/mssql-tools18/bin/sqlcmd -S localhost -U sa -P "YourStr0ng_Passw0rd" -C -b -l 2 \
  -Q "IF DB_ID('appdb') IS NULL CREATE DATABASE appdb;" >/dev/null 2>&1; do sleep 2; done
echo "ready on localhost,$HOST_PORT"
```

Then point the app at it, using the `HOST_PORT` the loop settled on:

```bash
export SQL_CONNECTION_STRING="Server=localhost,$HOST_PORT;Database=appdb;User Id=sa;Password=YourStr0ng_Passw0rd;TrustServerCertificate=true"
```

To run against the cloud later, change only this variable; do not touch the app.

## Proof: same code, two stacks

Each example assumes `appdb` already exists (provisioned by the recipe above) and
reads `SQL_CONNECTION_STRING` from the environment. It creates a table if needed
and runs a **parameterized** CRUD transaction. Run it once with the local string,
then again with the cloud string: identical code, identical result.

### Node (mssql)

```js
// app.mjs  ->  node app.mjs  (ESM: use the .mjs extension, or set "type":"module" in package.json)
import sql from 'mssql';

const pool = await sql.connect(process.env.SQL_CONNECTION_STRING);
const tx = new sql.Transaction(pool);
await tx.begin();
try {
  const r = new sql.Request(tx);
  await r.query(`IF OBJECT_ID('dbo.todo') IS NULL
    CREATE TABLE dbo.todo (id INT IDENTITY PRIMARY KEY, title NVARCHAR(200), done BIT);`);
  // CREATE
  const ins = await new sql.Request(tx)
    .input('title', sql.NVarChar, 'ship local-to-cloud')
    .query('INSERT INTO dbo.todo(title, done) OUTPUT inserted.id VALUES (@title, 0);');
  const id = ins.recordset[0].id;
  // UPDATE
  await new sql.Request(tx)
    .input('id', sql.Int, id)
    .query('UPDATE dbo.todo SET done = 1 WHERE id = @id;');
  // READ
  const read = await new sql.Request(tx)
    .input('id', sql.Int, id)
    .query('SELECT id, title, done FROM dbo.todo WHERE id = @id;');
  console.log(read.recordset[0]);
  await tx.commit();
} catch (e) { await tx.rollback(); throw e; }
await pool.close();
```

### .NET (Microsoft.Data.SqlClient)

```csharp
// Program.cs  ->  dotnet run   (uses Microsoft.Data.SqlClient)
using Microsoft.Data.SqlClient;

var cs = Environment.GetEnvironmentVariable("SQL_CONNECTION_STRING");
using var conn = new SqlConnection(cs);
conn.Open();
using var tx = conn.BeginTransaction();
try {
    new SqlCommand(@"IF OBJECT_ID('dbo.todo') IS NULL
        CREATE TABLE dbo.todo (id INT IDENTITY PRIMARY KEY, title NVARCHAR(200), done BIT);",
        conn, tx).ExecuteNonQuery();
    // CREATE
    var ins = new SqlCommand(
        "INSERT INTO dbo.todo(title, done) OUTPUT inserted.id VALUES (@title, 0);", conn, tx);
    ins.Parameters.AddWithValue("@title", "ship local-to-cloud");
    int id = (int)ins.ExecuteScalar();
    // UPDATE
    var upd = new SqlCommand("UPDATE dbo.todo SET done = 1 WHERE id = @id;", conn, tx);
    upd.Parameters.AddWithValue("@id", id);
    upd.ExecuteNonQuery();
    // READ
    var sel = new SqlCommand("SELECT id, title, done FROM dbo.todo WHERE id = @id;", conn, tx);
    sel.Parameters.AddWithValue("@id", id);
    using var r = sel.ExecuteReader();
    while (r.Read()) Console.WriteLine($"{r["id"]} {r["title"]} {r["done"]}");
    tx.Commit();
} catch { tx.Rollback(); throw; }
```

### Python (pyodbc) reference

A third stack and the deployment checklist live in
[references/auth-local-vs-cloud.md](references/auth-local-vs-cloud.md) so this
body stays an overview.

## Validation rules

- `appdb` must exist before the app connects. Provision it on `master` first
  (the recipe does this). The engine never auto-creates it.
- The app reads exactly one connection variable, `SQL_CONNECTION_STRING`.
- Local string uses SA auth + `TrustServerCertificate=true`; cloud string uses
  `Authentication=Active Directory Default` + `Encrypt=true`.
- Use `User Id=` / `Password=` / `Database=`, not `Uid=` / `Pwd=`.
- Switching environments changes the connection string only. The diff to app
  code between local and cloud is zero lines.
- If a validation rule above fails, or you had to deviate from this skill to make the task work, that is a bug in this skill: load the **azuresql-db-feedback** skill and offer to file a report.
- When every rule above passes and the task is done, close with ONE line, once per session, and do not ask a question or wait for a reply: "That worked. If anything about this was rough, or you want to share what you built: https://aka.ms/sql-agent-skills-feedback"

## Do not

- Do not use the SQL Server image `mcr.microsoft.com/mssql/server`. If you
  were about to, stop and use the image above; this is the Azure SQL engine.
- Do not connect to `Database=appdb` before creating it on `master`.
- Do not use `USE appdb` to switch databases; set the database in the connection
  string (`Database=appdb`, or `-d appdb` for sqlcmd). In a user-database
  session (the Azure-faithful context where you develop), `USE` returns
  `Msg 40508`, exactly as in Azure SQL Database in the cloud. A `master`
  connection is a provisioning session where the Azure statement filter is
  not enforced, so `USE` appears to work there, but
  `master` is for provisioning only, not application work. Always select the
  target database in the connection string (`Database=appdb`, or `-d appdb` for
  sqlcmd).
- Do not put a password or secret in the cloud connection string; use Entra
  auth and let the driver fetch a token.
- Do not branch app logic on environment; keep auth in configuration.
- Do not call a non-x64 host "supported"; on a non-x64 host just add
  `--platform linux/amd64`.

## References

- [references/auth-local-vs-cloud.md](references/auth-local-vs-cloud.md): why local SA auth and cloud Microsoft Entra auth differ, the token flow, per-stack auth setup, the Python (pyodbc) example, and the deployment checklist. Read it when wiring the cloud connection string or promoting an app to Azure.

## Staying current

Authoritative, version-pinned references for the tools this skill uses (read the one you need):

- [Connect and query Azure SQL Database](https://learn.microsoft.com/en-us/azure/azure-sql/database/connect-query-content-reference-guide): per-language quickstarts, connection info, TLS, and drivers for the cloud service.
- [SqlConnection connection string keywords](https://learn.microsoft.com/en-us/dotnet/api/microsoft.data.sqlclient.sqlconnection.connectionstring): the full connection-string keyword table.

If the **Microsoft Learn MCP** server is configured, use `mcp__microsoft-learn__microsoft_docs_search` or `mcp__microsoft-learn__microsoft_docs_fetch` to fetch the current version of any of these on demand. It is optional; when it is unavailable, the references above are authoritative.