add the ability to retry database connections when they fail

Author: lovasoa

.env

@@ -1,2 +1,2 @@
 # Set COMPOSE_PROFILES to one of the following: postgres, mysql, mssql. If set to mssql, you will need to change the depends_on propery in docker-compose.yml
-COMPOSE_PROFILES=postgres
+COMPOSE_PROFILES=mssql

configuration.md

@@ -4,13 +4,14 @@ SQLPage can be configured through either [environment variables](https://en.wiki
 on a [JSON](https://en.wikipedia.org/wiki/JSON) file placed in `sqlpage/sqlpage.json`.
 
 | variable                                   | default                      | description                                                              |
-|--------------------------------------------|------------------------------|--------------------------------------------------------------------------|
+| ------------------------------------------ | ---------------------------- | ------------------------------------------------------------------------ |
 | `listen_on`                                | 0.0.0.0:8080                 | Interface and port on which the web server should listen                 |
 | `database_url`                             | sqlite://sqlpage.db?mode=rwc | Database connection URL                                                  |
 | `port`                                     | 8080                         | Like listen_on, but specifies only the port.                             |
 | `max_database_pool_connections`            | depends on the database      | How many simultaneous database connections to open at most               |
 | `database_connection_idle_timeout_seconds` | depends on the database      | Automatically close database connections after this period of inactivity |
 | `database_connection_max_lifetime_seconds` | depends on the database      | Always close database connections after this amount of time              |
+| `database_connection_retries`              | 6                            | Database connection attempts before giving up. Retries will happen every 5 seconds.           |
 | `sqlite_extensions`                        |                              | An array of SQLite extensions to load, such as `mod_spatialite`          |
 
 You can find an example configuration file in [`sqlpage/sqlpage.json`](./sqlpage/sqlpage.json).
@@ -26,5 +27,5 @@ but in uppercase.
 
 ```bash
 DATABASE_URL="sqlite:///path/to/my_database.db?mode=rwc"
-SQLITE_EXTENSIONS="mod_spatialite crypto define regexp" 
-```
+SQLITE_EXTENSIONS="mod_spatialite crypto define regexp"
+```

src/app_config.rs

@@ -21,18 +21,19 @@ pub struct AppConfig {
     #[serde(deserialize_with = "deserialize_socket_addr")]
     pub listen_on: SocketAddr,
     pub port: Option<u16>,
+
+    /// Number of times to retry connecting to the database after a failure when the server starts
+    /// up. Retries will happen every 5 seconds. The default is 6 retries, which means the server
+    /// will wait up to 30 seconds for the database to become available.
+    #[serde(default = "default_database_connection_retries")]
+    pub database_connection_retries: u32,
 }
 
 pub fn load() -> anyhow::Result<AppConfig> {
     let mut conf = Config::builder()
         .set_default("listen_on", "0.0.0.0:8080")?
         .add_source(config::File::with_name("sqlpage/sqlpage").required(false))
-        .add_source(
-            config::Environment::default()
-                .try_parsing(true)
-                .list_separator(" ")
-                .with_list_parse_key("sqlite_extensions"),
-        )
+        .add_source(env_config())
         .build()?
         .try_deserialize::<AppConfig>()
         .with_context(|| "Unable to load configuration")?;
@@ -42,6 +43,13 @@ pub fn load() -> anyhow::Result<AppConfig> {
     Ok(conf)
 }
 
+fn env_config() -> config::Environment {
+    config::Environment::default()
+        .try_parsing(true)
+        .list_separator(" ")
+        .with_list_parse_key("sqlite_extensions")
+}
+
 fn deserialize_socket_addr<'de, D: Deserializer<'de>>(
     deserializer: D,
 ) -> Result<SocketAddr, D::Error> {
@@ -80,6 +88,10 @@ fn default_database_url() -> String {
     prefix + ":memory:"
 }
 
+fn default_database_connection_retries() -> u32 {
+    6
+}
+
 #[cfg(test)]
 pub(crate) mod tests {
     use super::AppConfig;

src/webserver/database/mod.rs

@@ -217,10 +217,24 @@ impl Database {
         );
         set_custom_connect_options(&mut connect_options, config);
         log::info!("Connecting to database: {database_url}");
-        let connection = Self::create_pool_options(config, connect_options.kind())
-            .connect_with(connect_options)
-            .await
-            .with_context(|| format!("Unable to open connection to {database_url}"))?;
+        let mut retries = config.database_connection_retries;
+        let connection = loop {
+            match Self::create_pool_options(config, connect_options.kind())
+                .connect_with(connect_options.clone())
+                .await
+            {
+                Ok(c) => break c,
+                Err(e) => {
+                    if retries == 0 {
+                        return Err(anyhow::Error::new(e)
+                            .context(format!("Unable to open connection to {database_url}")));
+                    }
+                    log::warn!("Failed to connect to the database: {e:#}. Retrying in 5 seconds.");
+                    retries -= 1;
+                    tokio::time::sleep(Duration::from_secs(5)).await;
+                }
+            }
+        };
         log::debug!("Initialized database pool: {connection:#?}");
         Ok(Database { connection })
     }