Add slashing protection health check.

docs/HowTo/Configure-Slashing-Protection.md

@@ -144,6 +144,17 @@ You can include additional optional pruning configuration options. For example,
 
     Do not use slashing protection database pruning while [importing or exporting the database](#import-or-export-a-slashing-protection-database).
 
+## Slashing protection health check
+
+By default, Web3Signer performs a health check on the slashing protection database every 30000 milliseconds.
+To change the default value, configure the [`--slashing-protection-db-health-check-interval-milliseconds`](../Reference/CLI/CLI-Subcommands.md#slashing-protection-db-health-check-interval-milliseconds)
+command line option.
+
+The service responds with a `200` message if healthy, and `503` if unhealthy.
+
+You can also configure the health check timeout with the [`--slashing-protection-db-health-check-timeout-milliseconds`](../Reference/CLI/CLI-Subcommands.md#slashing-protection-db-health-check-timeout-milliseconds)
+command line option. The timeout defaults to 3000 milliseconds.
+
 <!-- links -->
 [slashing protection]: ../Concepts/Slashing-Protection.md
 [slashing protection database pruning]: #prune-the-slashing-protection-database

docs/HowTo/Get-Started/Start-Web3Signer.md

@@ -62,7 +62,8 @@ Start the client, for example [Teku] by specifying the Web3Signer details.
 
 ## Confirm Web3Signer is running
 
-Use the [`upcheck`](https://consensys.github.io/web3signer/web3signer-eth2.html#tag/Server-Status) endpoint to confirm Web3Signer is connected and running.
+Use the [`upcheck`](https://consensys.github.io/web3signer/web3signer-eth2.html#tag/Server-Status) endpoint
+to confirm Web3Signer is connected and running.
 
 !!! example
 
@@ -78,6 +79,9 @@ Use the [`upcheck`](https://consensys.github.io/web3signer/web3signer-eth2.html#
         200 OK
         ```
 
+Web3Signer by default also performs a health check on the
+[slashing protection database](../../HowTo/Configure-Slashing-Protection.md#slashing-protection-health-check).
+
 <!-- Links -->
 [Signing key configuration files]: ../Use-Signing-Keys.md
 [Teku]: https://docs.teku.consensys.net/en/latest/HowTo/External-Signer/Use-External-Signer/

docs/Reference/CLI/CLI-Subcommands.md

@@ -691,6 +691,67 @@ Possible values are:
 | `ropsten`    | Consensus layer | Test       | Multi-client testnet.                            |
 | `gnosis`     | Consensus layer | Test       | Multi-client testnet.                            |
 
+#### `slashing-protection-db-health-check-interval-milliseconds`
+
+=== "Syntax"
+
+    ```bash
+    --slashing-protection-db-health-check-interval-milliseconds=<INTERVAL>
+    ```
+
+=== "Example"
+
+    ```bash
+    --slashing-protection-db-health-check-interval-milliseconds=20000
+    ```
+
+=== "Environment variable"
+
+    ```bash
+    WEB3SIGNER_ETH2_SLASHING_PROTECTION_DB_HEALTH_CHECK_INTERVAL_MILLISECONDS=20000
+    ```
+
+=== "Configuration file"
+
+    ```bash
+    eth2.slashing-protection-db-health-check-interval-milliseconds: 20000
+    ```
+
+Milliseconds between the slashing protection database health checks. The default is 30000.
+
+The service responds with a `200` message if healthy, and `503` if unhealthy.
+
+#### `slashing-protection-db-health-check-timeout-milliseconds`
+
+=== "Syntax"
+
+    ```bash
+    --slashing-protection-db-health-check-timeout-milliseconds=<INTERVAL>
+    ```
+
+=== "Example"
+
+    ```bash
+    --slashing-protection-db-health-check-timeout-milliseconds=2000
+    ```
+
+=== "Environment variable"
+
+    ```bash
+    WEB3SIGNER_ETH2_SLASHING_PROTECTION_DB_HEALTH_CHECK_TIMEOUT_MILLISECONDS=2000
+    ```
+
+=== "Configuration file"
+
+    ```bash
+    eth2.slashing-protection-db-health-check-timeout-milliseconds: 2000
+    ```
+
+Milliseconds after which to fail the database health check. For example, if the health check
+connects to the slashing protection database, but does not report back in a timely manner.
+
+The default is 3000.
+
 #### `slashing-protection-db-password`
 
 === "Syntax"