License

The product ships with an RSA-signed license file (license.lic). The vendor holds the private key; the application bundles only the public key and verifies the signature on every start.

A license buys support, not features. The application is fully functional without one — you can add servers, edit alert rules, run index maintenance, everything. The license records who holds a support entitlement and how long it runs. The software itself is perpetual: when the support period ends, nothing stops working.

How licensing works

• appsettings.json:Licensing:PublicKeyBase64 — the vendor's RSA-2048 public key. Shipped with the binary. Don't change this unless the vendor reissues a new key generation.
• appsettings.json:Licensing:LicenseFilePath — path to the license envelope file. Default license.lic (next to the binary).
• The license envelope is a small JSON document containing customer name, edition, support expiry date, and a base64 RSA signature. The app re-verifies the signature on every start and reports the result — it never blocks anything.

Installing a license

1. The vendor sends you license.lic.
2. Drop it next to the binary (Windows: C:\Apps\SqlServerHealthMonitor\license.lic; Linux: /opt/sshm/license.lic).
3. Restart the app.
4. Watch the startup log — you should see:

   License: support for Acme Corp (edition Standard) runs until 2027-06-30, 392 days remaining.
   

5. Visit /Settings/License to verify the same info in the UI.

If the log says:

License: Invalid — signature mismatch. Support status unknown; no features are restricted.

…either the file is corrupted in transit, or the public key in appsettings.json doesn't match the private key that signed the file. Re-download the license; if that fails, the public key probably needs to be reissued by the vendor.

Rotating / renewing

A renewed license is a new license.lic file with a later ExpiresAt. Replace the file and restart — no app version change needed.

You can also install a renewal via the UI: /Settings/License → upload the new file. The change is hot — no restart required.

Generating a new license (vendor side)

Vendor workflow only — for the operator side this is "don't touch":

# Generate the keypair (one-time, vendor keeps the private half FOREVER).
# Writes license-private-key.xml to the current dir and prints the public key.
dotnet run --project tools/LicenseGenerator -- genkey

# Sign a license for a customer. Positional args:
#   sign <private-key.xml> <customer> <expires-yyyy-mm-dd> [edition] [maxServers]
#   maxServers: recorded in the envelope and shown on the license page, but NOT
#               enforced — nothing in the product gates on it. 0 or omitted = unset.
dotnet run --project tools/LicenseGenerator -- sign \
    license-private-key.xml "Acme Corp" 2027-06-30 Standard 0

# A license that names a server count (recorded only — nothing enforces it):
dotnet run --project tools/LicenseGenerator -- sign \
    license-private-key.xml "Acme Corp (Demo)" 2099-12-31 Demo 3

# The signed file is written as license.lic in the current directory. Send it to
# the customer; paste the printed public key into appsettings.json:Licensing:PublicKeyBase64.

If the vendor loses the private key: every previously-issued license stays valid (existing installs continue to verify), but new licenses can't be signed unless you generate a new keypair and ship an updated build with the new public key. That's an outage for new sales until the next release goes out.

What happens without a license, or with an expired one

Nothing stops working. There is no read-only mode, no feature gate and no server cap — every function is available whether a license is installed or not. What changes is only what the product can tell you about your support entitlement:

State	What you see
Valid	/Settings/License shows the customer, edition and remaining support days. No banner.
Missing	Nothing at all. An unlicensed install is a normal, supported state.
Expired	Administrators get an informational banner saying support ended on that date, and that features are unaffected.
Invalid / Tampered	Administrators get an informational banner saying the file could not be read, so the support status is unknown.

If you are looking for the code: LicenseStatus in Services/LicenseService.cs carries the rule in a comment, and deliberately exposes no flag that a page could gate on.