diff --git a/backend/api_server/src/blog/cron/check_update.rs b/backend/api_server/src/blog/cron/check_update.rs
index f2fe6a9..5f016d6 100644
--- a/backend/api_server/src/blog/cron/check_update.rs
+++ b/backend/api_server/src/blog/cron/check_update.rs
@@ -1,6 +1,7 @@
-use dirs::home_dir;
 use std::env;
 
+use dirs::home_dir;
+
 pub fn task() {
     // get dir
     let git_work_dir_path = &env::var("GIT_WORK_DIR").unwrap_or_else(|e| {
diff --git a/backend/api_server/src/init.rs b/backend/api_server/src/init.rs
deleted file mode 100644
index c240d89..0000000
--- a/backend/api_server/src/init.rs
+++ /dev/null
@@ -1,23 +0,0 @@
-use crate::logger;
-use std::{env, panic};
-
-use tracing_appender::non_blocking::WorkerGuard;
-
-pub fn logger_init() -> (WorkerGuard, WorkerGuard) {
-    logger::init()
-}
-
-pub fn load_env() {
-    if let Some(env_file) = env::args().nth(1) {
-        match dotenv::from_filename(&env_file) {
-            Ok(_) => {
-                println!("[info] env loaded from {}, starting up", env_file);
-            }
-            Err(e) => {
-                panic!("[fatal] failed to read {}: {}", env_file, e);
-            }
-        }
-    } else {
-        println!("[info] no .env file referred, starting up")
-    }
-}
diff --git a/backend/api_server/src/init/database.rs b/backend/api_server/src/init/database.rs
new file mode 100644
index 0000000..e403269
--- /dev/null
+++ b/backend/api_server/src/init/database.rs
@@ -0,0 +1,38 @@
+use std::env;
+use std::error::Error;
+use std::str::FromStr;
+
+use constants::config::database::{default_value, var_name};
+use sqlx::postgres::{PgConnectOptions, PgPoolOptions};
+use sqlx::{ConnectOptions, Pool, Postgres};
+use tracing::info;
+
+pub async fn init() -> Result<Pool<Postgres>, Box<dyn Error>> {
+    let db_connect_option = PgConnectOptions::from_str(&parse_db_uri())
+        .unwrap()
+        .disable_statement_logging();
+    Ok(PgPoolOptions::new().connect_with(db_connect_option).await?)
+}
+
+fn parse_db_uri() -> String {
+    env::var(var_name::URI).unwrap_or_else(|_| {
+        info!(
+            "`{}` env var is not set, \
+            using `{}`, `{}`, `{}`, `{}` and `{}`",
+            var_name::URI,
+            var_name::USERNAME,
+            var_name::PASSWORD,
+            var_name::HOST,
+            var_name::PORT,
+            var_name::DBNAME
+        );
+        let postgres_user = env::var(var_name::USERNAME).unwrap_or(default_value::USERNAME.into());
+        let postgres_password =
+            env::var(var_name::PASSWORD).unwrap_or(default_value::PASSWORD.into());
+        let db_host = env::var(var_name::HOST).unwrap_or(default_value::HOST.into());
+        let db_port = env::var(var_name::PORT).unwrap_or(default_value::PORT.into());
+        let postgres_db = env::var(var_name::DBNAME).unwrap_or(default_value::DBNAME.into());
+        let db_type = default_value::DATABASE_TYPE;
+        format!("{db_type}://{postgres_user}:{postgres_password}@{db_host}:{db_port}/{postgres_db}")
+    })
+}
diff --git a/backend/api_server/src/logger.rs b/backend/api_server/src/init/logger.rs
similarity index 63%
rename from backend/api_server/src/logger.rs
rename to backend/api_server/src/init/logger.rs
index 7dc26e2..5fd56b4 100644
--- a/backend/api_server/src/logger.rs
+++ b/backend/api_server/src/init/logger.rs
@@ -2,6 +2,7 @@ use std::path::Path;
 use std::{env, io};
 
 use chrono::Local;
+use constants::config::general::{default_value, var_name};
 use dirs::home_dir;
 use tracing::info;
 use tracing_appender::{non_blocking, non_blocking::WorkerGuard, rolling};
@@ -25,33 +26,26 @@ impl FormatTime for LocalTimer {
 type _LogWriter = dyn for<'writer> MakeWriter<'writer, Writer = dyn io::Write + 'static> + 'static;
 
 pub fn init() -> (WorkerGuard, WorkerGuard) {
-    let log_path = &env::var("LOG_ROOT_DIR").unwrap_or_else(|e| {
-        if let Ok(default_log_path) = env::var("WORK_DIR") {
-            if default_log_path.starts_with('~') {
-                let home_path = home_dir()
-                    .expect("[fatal] unable to locate home dir with parsing env `WORK_DIR`, try to use absolute path instead");
-                home_path
-                    .join(default_log_path.strip_prefix("~/").unwrap())
-                    .into_os_string()
-                    .into_string()
-                    .expect("[fatal] failed to parse env `WORK_DIR`, try to use absolute path instead")
+    let log_path = match env::var(var_name::LOG_DIR) {
+        Ok(path) => Path::new(&path).to_path_buf(),
+        Err(_) => {
+            let path = if let Ok(default_log_path) = env::var(var_name::WORK_DIR) {
+                expand_home_path(default_log_path)
             } else {
-                default_log_path
-            }
-        } else {
-            panic!("[fatal] failed to parse env `LOG_ROOT_DIR`: {}", e);
+                let fallback_path = expand_home_path(default_value::WORK_DIR.to_string());
+                println!(
+                    "[warn] unset env var `{}` and `{}`, trying to log on fallback path: {}/log",
+                    var_name::LOG_DIR,
+                    var_name::WORK_DIR,
+                    fallback_path
+                );
+                fallback_path
+            };
+            Path::new(&path).join("log")
         }
-    });
-
-    let log_path = Path::new(log_path)
-        .join("log")
-        .join("backend")
-        .into_os_string()
-        .into_string()
-        .unwrap_or_else(|e| panic!("[fatal] failed to parse {:?}", e));
+    };
 
     let (info_log_writer, info_guard) = non_blocking(rolling::never(&log_path, "info.log"));
-
     let (err_log_writer, error_guard) = non_blocking(rolling::never(&log_path, "error.log"));
 
     let info_format = tracing_subscriber::fmt::format()
@@ -70,9 +64,6 @@ pub fn init() -> (WorkerGuard, WorkerGuard) {
         .with_source_location(true)
         .with_timer(LocalTimer);
 
-    // let default_filter = tracing_subscriber::filter::EnvFilter::try_from_default_env()
-    //     .unwrap_or_else(|_| "tower_http=debug,axum::rejection=trace".into());
-
     let subscribers = Registry::default()
         .with(
             fmt::Layer::default()
@@ -95,8 +86,21 @@ pub fn init() -> (WorkerGuard, WorkerGuard) {
     tracing::subscriber::set_global_default(subscribers)
         .expect("[fatal] failed to setup logging system");
 
-    info!("module started: logger");
-    info!("logging to dir: {}", log_path);
+    info!("logging to dir: {}", log_path.to_str().unwrap());
 
     (info_guard, error_guard)
 }
+
+fn expand_home_path(path: String) -> String {
+    if path.starts_with('~') {
+        let home_path = home_dir()
+            .unwrap_or_else(|| panic!("[fatal] unable to locate home dir when parsing env `{}`, try to use absolute path instead", var_name::WORK_DIR));
+        home_path
+            .join(path.strip_prefix("~/").unwrap())
+            .into_os_string()
+            .into_string()
+            .unwrap()
+    } else {
+        path
+    }
+}
diff --git a/backend/api_server/src/init/mod.rs b/backend/api_server/src/init/mod.rs
new file mode 100644
index 0000000..e65de59
--- /dev/null
+++ b/backend/api_server/src/init/mod.rs
@@ -0,0 +1,45 @@
+mod database;
+pub mod logger;
+pub mod server;
+
+use macros::panic_with_log;
+use std::{env, panic};
+use tracing::{info, Level};
+
+pub fn load_env() {
+    if let Some(env_file) = env::args().nth(1) {
+        match dotenv::from_filename(&env_file) {
+            Ok(_) => {
+                println!("[info] env loaded from {}, starting up", env_file);
+            }
+            Err(e) => {
+                panic!("[fatal] failed to read {}: {}", env_file, e);
+            }
+        }
+    } else {
+        println!("[info] no .env file referred, starting up")
+    }
+}
+
+pub async fn start() {
+    let db_pool = match database::init().await {
+        Ok(pool) => {
+            info!("database connection pool initialized");
+            pool
+        }
+        Err(e) => {
+            panic_with_log!(
+                Level::ERROR,
+                "database connection pool failed to initialize: {}",
+                e
+            );
+        }
+    };
+
+    match server::start(db_pool).await {
+        Ok(_) => {}
+        Err(e) => {
+            panic_with_log!(Level::ERROR, "server panicked: {}", e)
+        }
+    }
+}
diff --git a/backend/api_server/src/init/server.rs b/backend/api_server/src/init/server.rs
new file mode 100644
index 0000000..703a043
--- /dev/null
+++ b/backend/api_server/src/init/server.rs
@@ -0,0 +1,52 @@
+use std::env;
+use std::error::Error;
+use std::num::ParseIntError;
+use std::process::exit;
+
+use crate::blog;
+use axum::Router;
+use constants::config::server::{default_value, var_name};
+use macros::panic_with_log;
+use sqlx::{Pool, Postgres};
+use tracing::{error, info, warn, Level};
+
+pub async fn start(db_pool: Pool<Postgres>) -> Result<(), Box<dyn Error>> {
+    let app = Router::new()
+        .nest("/blog", blog::get_router())
+        .with_state(db_pool);
+
+    let port: u32 = match env::var(var_name::PORT) {
+        Ok(value) => value.parse().unwrap_or_else(|e: ParseIntError| {
+            warn!(
+                "failed to parse `{}`, using default port: {}",
+                var_name::PORT,
+                e.to_string()
+            );
+            default_value::PORT
+        }),
+        Err(_) => default_value::PORT,
+    };
+
+    let listener =
+        match tokio::net::TcpListener::bind(format!("{}:{}", default_value::HOST, port)).await {
+            Ok(listener) => {
+                info!("server started on {}:{}", default_value::HOST, port);
+                listener
+            }
+            Err(e) => {
+                panic_with_log!(
+                    Level::ERROR,
+                    "failed to start server on {}:{}: {}",
+                    default_value::HOST,
+                    port,
+                    e.to_string()
+                );
+            }
+        };
+
+    axum::serve(listener, app).await.unwrap_or_else(|e| {
+        error!("failed to start axum: {}", e.to_string());
+        exit(1);
+    });
+    Ok(())
+}
diff --git a/backend/api_server/src/main.rs b/backend/api_server/src/main.rs
index c1431c4..5cdd2e5 100644
--- a/backend/api_server/src/main.rs
+++ b/backend/api_server/src/main.rs
@@ -1,21 +1,12 @@
-use macros::panic_with_log;
-use tracing::Level;
-
 mod blog;
 mod init;
-mod logger;
 mod scheduler;
-mod server;
 
 #[tokio::main]
 async fn main() {
     init::load_env();
-    let _guards = init::logger_init();
 
-    match server::start().await {
-        Ok(_) => {}
-        Err(e) => {
-            panic_with_log!(Level::ERROR, "failed to start server: {}", e);
-        }
-    };
+    let _guards = init::logger::init();
+
+    init::start().await;
 }
diff --git a/backend/api_server/src/server.rs b/backend/api_server/src/server.rs
deleted file mode 100644
index 047eae1..0000000
--- a/backend/api_server/src/server.rs
+++ /dev/null
@@ -1,88 +0,0 @@
-use std::env;
-use std::error::Error;
-use std::num::ParseIntError;
-use std::process::exit;
-use std::str::FromStr;
-
-use crate::blog;
-use axum::Router;
-use macros::panic_with_log;
-use sqlx::{
-    postgres::{PgConnectOptions, PgPoolOptions},
-    ConnectOptions,
-};
-use tracing::{error, info, warn, Level};
-
-pub async fn start() -> Result<(), Box<dyn Error>> {
-    let port: u32 = match env::var("BACKEND_PORT") {
-        Ok(value) => value.parse().unwrap_or_else(|e: ParseIntError| {
-            warn!("failed to parse BACKEND_PORT: {}", e.to_string());
-            3001
-        }),
-        Err(_) => 3001,
-    };
-
-    let db_connect_option = PgConnectOptions::from_str(&parse_db_uri())
-        .unwrap()
-        .disable_statement_logging();
-
-    let db_pool = match PgPoolOptions::new().connect_with(db_connect_option).await {
-        Ok(pool) => {
-            info!("database connected");
-            pool
-        }
-        Err(e) => {
-            error!("failed to load database: {}", e.to_string());
-            exit(1);
-        }
-    };
-
-    // cron task
-    // let scheduler = Scheduler::new();
-    // let test_str = "hello world".to_string();
-    // scheduler.insert(
-    //     BasicTask::new(
-    //         move || blog::cron::check_update::task(test_str.clone()),
-    //         "* * * * * *",
-    //     )?
-    //     .to_task(),
-    // )?;
-
-    // http server
-    let app = Router::new()
-        .nest("/blog", blog::get_router())
-        .with_state(db_pool);
-
-    let listener = match tokio::net::TcpListener::bind(format!("0.0.0.0:{}", port)).await {
-        Ok(listener) => {
-            info!("server started on 0.0.0.0:{}", port);
-            listener
-        }
-        Err(e) => {
-            panic_with_log!(
-                Level::ERROR,
-                "failed to start server on 0.0.0.0:{}: {}",
-                port,
-                e.to_string()
-            );
-        }
-    };
-
-    axum::serve(listener, app).await.unwrap_or_else(|e| {
-        error!("failed to start axum: {}", e.to_string());
-        exit(1);
-    });
-    Ok(())
-}
-
-fn parse_db_uri() -> String {
-    let postgres_user = env::var("POSTGRES_USER").unwrap_or("".to_string());
-    let postgres_password = env::var("POSTGRES_PASSWORD").unwrap_or("".to_string());
-    let db_host = env::var("DB_HOST").unwrap_or("localhost".to_string());
-    let db_port = env::var("DB_PORT")
-        .unwrap_or("5432".to_string())
-        .to_string();
-    let postgres_db = env::var("POSTGRES_DB").unwrap_or("nocturne".to_string());
-
-    format!("postgresql://{postgres_user}:{postgres_password}@{db_host}:{db_port}/{postgres_db}")
-}
diff --git a/backend/constants/src/config.rs b/backend/constants/src/config.rs
new file mode 100644
index 0000000..4584402
--- /dev/null
+++ b/backend/constants/src/config.rs
@@ -0,0 +1,43 @@
+// Database related
+pub mod database {
+    pub mod var_name {
+        pub const URI: &str = "DATABASE_URL";
+        pub const USERNAME: &str = "POSTGRES_USER";
+        pub const PASSWORD: &str = "POSTGRES_PASSWORD";
+        pub const HOST: &str = "POSTGRES_HOST";
+        pub const PORT: &str = "POSTGRES_PORT";
+        pub const DBNAME: &str = "POSTGRES_DB";
+    }
+
+    pub mod default_value {
+        pub const USERNAME: &str = "";
+        pub const PASSWORD: &str = "";
+        pub const HOST: &str = "localhost";
+        pub const PORT: &str = "5432";
+        pub const DBNAME: &str = "nocturne";
+        pub const DATABASE_TYPE: &str = "postgresql";
+    }
+}
+
+pub mod server {
+    pub mod var_name {
+        pub const PORT: &str = "BACKEND_PORT";
+        pub const HOST: &str = "BACKEND_HOST";
+    }
+
+    pub mod default_value {
+        pub const PORT: u32 = 3001;
+        pub const HOST: &str = "0.0.0.0";
+    }
+}
+
+pub mod general {
+    pub mod var_name {
+        pub const LOG_DIR: &str = "LOG_DIR";
+        pub const WORK_DIR: &str = "WORK_DIR";
+    }
+
+    pub mod default_value {
+        pub const WORK_DIR: &str = "~/.nocturne";
+    }
+}
diff --git a/backend/constants/src/lib.rs b/backend/constants/src/lib.rs
index f5cd248..1b58b94 100644
--- a/backend/constants/src/lib.rs
+++ b/backend/constants/src/lib.rs
@@ -1,2 +1,3 @@
 pub mod blog;
+pub mod config;
 pub mod time;