add: implement basic server

Cargo.lock

@@ -654,9 +654,9 @@ dependencies = [
 
 [[package]]
 name = "libc"
-version = "0.2.176"
+version = "0.2.171"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "58f929b4d672ea937a23a1ab494143d968337a5f47e56d0815df1e0890ddf174"
+checksum = "c19937216e9d3aa9956d9bb8dfc0b0c8beb6058fc4f7a4dc4d850edf86a237d6"
 
 [[package]]
 name = "libredox"

Dockerfile

@@ -1,12 +0,0 @@
-# Build Stage
-FROM rust:latest AS builder
-WORKDIR /app
-COPY . .
-RUN cargo build --release
-
-# Runtime Stage
-FROM debian:stable-slim
-WORKDIR /app
-COPY --from=builder /app/target/release/handler .
-COPY --from=builder /app/target/release/skubelb .
-CMD ["./handler"]

Makefile

@@ -1,16 +0,0 @@
-MAJOR_VERSION = 0
-MINOR_VERSION = 0
-PATH_VERSION = 1
-
-TAG = $(MAJOR_VERSION).$(MINOR_VERSION).$(PATH_VERSION)
-
-build:
-	docker build . -t skubelb-handler:$(TAG)
-	docker tag skubelb-handler:$(TAG) us-west4-docker.pkg.dev/nixernetes/images/skubelb-handler:$(TAG)
-
-kube:
-	cat kubernetes.yaml.tmpl | sed 's/TAG/$(TAG)/' > kubernetes.yaml
-
-deploy: build kube
-	docker push us-west4-docker.pkg.dev/nixernetes/images/skubelb-handler:$(TAG)
-	kubectl apply -f kubernetes.yaml

README.md

@@ -6,173 +6,14 @@ open a port on all nodes. When the request lands on any node,
 it is forwarded to the correct pod via the network mesh kubernetes
 is using. In theory, there is one a hop penalty.
 
-But lets be honest. You're running with a single LB, probably on a
-GCE free tier N1 VM. That extra hop doesn't matter.
+But lets be honest. You're running with a single LB, probably a GCE free
+tier N1 VM. That extra hop doesn't matter.
 
 ## Config
 
 Configure nginx to do what you want, test it. Use any Node IP for your testing.
-This will become the 'template_dir' in the argument to the LB.
+This tool accepts an argument (rewrite_string) which will be replaced using these rules:
 
-Move that directory (i.e., `/etc/nginx`) to somewhere new,
-(i.e. `/etc/nginx-template/`).
+1. For each line that contains rewrite string:
+2. Copy the line once per node IP, replacing the string with host IPs
 
-Make a workspace directory for this tool; it will write configs to this folder
-before updating the symlink you created above. It needs to be persistent so on
-server reboot the service starts ok (i.e., `mkdir /var/skubelb/`).
-
-Create a symlink in the workspace which will point to the 'active' configuration;
-this will be updated by the tool (i.e., `ln -s /etc/nginx-template /var/skubelb/nginx`).
-Make a symlink from the old config directory to that symlink (i.e., 
-`ln -s /var/skubelb/nginx /etc/nginx`). Two layers are symlinks are used so we can
-have a non-root user run the rool when we setup the service.
-
-Make sure the user running the tool has read access to the template folder, read-write
-access to the workspace folder and config symlink.
-
-Run the server with a command like:
-
-```sh
-skubelb --needle some_node_ip \
-    --workspace_dir /var/skubelb \
-    --config_symlink /var/skubelb/nginx \
-    --template_dir /etc/nginx-template
-    --listen 0.0.0.0:8888
-```
-
-Replacing `some_node_ip` with the node IP you used during the initial setup.
-
-Next, configure the Kubernetes nodes to POST `http://loadbalancer:8888/register/${NODE_IP}` when
-they started, and DELETE `http://loadbalancer:8888/register/${NODE_IP}` when they shutdown. The easiest
-way to do this is with a daemonset; see the example below, or in daemon_set.yaml.
-
-#### Running as a system service
-
-Setup a user to run the service; make that user
-with `useradd -M skubelb`, Prevent logins with `usermod -L skubelb`.
-
-Make a workspace dir, `mkdir /var/skubelb/`, and give access to the
-daemon user, `chown skubelb:skubelb /var/skubelb/`.
-
-Add the systemd config to `/etc/systemd/system/skubelb.service`:
-
-```toml
-[Unit]
-Description=Simple Kubernetes Load Balancer
-After=network.target
-StartLimitIntervalSec=0
-
-[Service]
-Type=simple
-Restart=always
-RestartSec=1
-User=skubelb
-ExecStart=/usr/local/bin/skubelb --needle some_node_ip \
-    --workspace-dir /var/skubelb \
-    --config-symlink /var/skubelb/nginx \
-    --template-dir /etc/nginx-template \
-    --listen 0.0.0.0:8888 \
-    --reload-cmd '/usr/bin/sudo systemctl reload nginx'
-
-[Install]
-WantedBy=multi-user.target
-```
-
-Make sure you update `--needle some_node_ip` with something
-like `--needle 123.44.55.123`. The IP of node you tested with.
-
-### Sample Kubernets configuration
-
-Deploy this [daemon set](https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/)
-to your cluster, replacing `lb_address` with the address of your load balancer.
-
-```yaml
-apiVersion: apps/v1
-kind: DaemonSet
-metadata:
-  name: skubelb
-  namespace: skubelb
-  labels:
-    k8s-app: skubelb
-spec:
-  selector:
-    matchLabels:
-      name: skubelb
-  template:
-    metadata:
-      labels:
-        name: skubelb
-    spec:
-      tolerations:
-      # these tolerations are to have the daemonset runnable on control plane nodes
-      # remove them if your control plane nodes should not run pods
-      - key: node-role.kubernetes.io/control-plane
-        operator: Exists
-        effect: NoSchedule
-      - key: node-role.kubernetes.io/master
-        operator: Exists
-        effect: NoSchedule
-      containers:
-      - name: skubelb
-        image: alpine/curl:latest
-        env:
-        - name: NODE_IP
-          valueFrom:
-            fieldRef:
-              fieldPath: status.hostIP
-        command: ['sh', '-c', 'echo "Wait for heat death of universe" && sleep 999999d']
-        lifecycle:
-          preStop:
-            exec:
-              command:
-              - sh
-              - "-c"
-              - "curl -X POST 10.128.0.2:8888/register/${NODE_IP}"
-          postStart:
-            exec:
-              command:
-              - sh
-              - "-c"
-              - "curl -X POST 10.128.0.2:8888/register/${NODE_IP}"
-        resources:
-          limits:
-            memory: 200Mi
-          requests:
-            cpu: 10m
-            memory: 100Mi
-      terminationGracePeriodSeconds: 30
-```
-
-NOTE: you should need to make an entry in the firewall to allow this request through. It is very important that the firewall entry has a source filter; it should only be allowed from the Kubernetes cluster. Nginx will forward traffic to any host that registers, and this could easily become a MitM vulnerability.
-
-## Other tips
-
-### Use 'upstream' in nginx
-
-Do this:
-
-```
-upstream hosts {
-        server 10.182.0.36:30004;
-        server 10.182.0.39:30004;
-}
-server {
-        server_name git.tipsy.codes tipsy.codes;
-
-        location / {
-                proxy_pass http://hosts;
-        }
-}
-```
-
-Rather than just writing out the IP in the proxy_pass.
-
-### visudo to only allow the nginx reload command
-
-Use `sudo visudo` to update the sudoers file and add this line:
-
-```
-skubelb ALL=(root) NOPASSWD: /usr/bin/systemctl reload nginx
-```
-
-This will prevent the user from running commands other than reload.

daemon_set.yaml

@@ -1,54 +0,0 @@
-apiVersion: apps/v1
-kind: DaemonSet
-metadata:
-  name: skubelb
-  namespace: skubelb
-  labels:
-    k8s-app: skubelb
-spec:
-  selector:
-    matchLabels:
-      name: skubelb
-  template:
-    metadata:
-      labels:
-        name: skubelb
-    spec:
-      tolerations:
-      # these tolerations are to have the daemonset runnable on control plane nodes
-      # remove them if your control plane nodes should not run pods
-      - key: node-role.kubernetes.io/control-plane
-        operator: Exists
-        effect: NoSchedule
-      - key: node-role.kubernetes.io/master
-        operator: Exists
-        effect: NoSchedule
-      containers:
-      - name: skubelb
-        image: alpine/curl:latest
-        env:
-        - name: NODE_IP
-          valueFrom:
-            fieldRef:
-              fieldPath: status.hostIP
-        command: ['sh', '-c', 'echo "Wait for heat death of universe" && sleep 999999d']
-        lifecycle:
-          preStop:
-            exec:
-              command:
-              - sh
-              - "-c"
-              - "curl -X POST 10.128.0.2:8888/register/${NODE_IP}"
-          postStart:
-            exec:
-              command:
-              - sh
-              - "-c"
-              - "curl -X POST 10.128.0.2:8888/register/${NODE_IP}"
-        resources:
-          limits:
-            memory: 200Mi
-          requests:
-            cpu: 10m
-            memory: 100Mi
-      terminationGracePeriodSeconds: 30

kubernetes.yaml

@@ -1,41 +0,0 @@
-apiVersion: apps/v1
-kind: DaemonSet
-metadata:
-  name: skubelb
-  namespace: skubelb
-  labels:
-    k8s-app: skubelb
-spec:
-  selector:
-    matchLabels:
-      name: skubelb
-  template:
-    metadata:
-      labels:
-        name: skubelb
-    spec:
-      tolerations:
-      # these tolerations are to have the daemonset runnable on control plane nodes
-      # remove them if your control plane nodes should not run pods
-      - key: node-role.kubernetes.io/control-plane
-        operator: Exists
-        effect: NoSchedule
-      - key: node-role.kubernetes.io/master
-        operator: Exists
-        effect: NoSchedule
-      containers:
-      - name: skubelb
-        image: us-west4-docker.pkg.dev/nixernetes/images/skubelb-handler:0.0.1
-        env:
-        - name: NODE_IP
-          valueFrom:
-            fieldRef:
-              fieldPath: status.hostIP
-        command: ["sh", "-c", "./handler -s 10.128.0.2:8888 -l ${NODE_IP}"]
-        resources:
-          limits:
-            memory: 200Mi
-          requests:
-            cpu: 10m
-            memory: 100Mi
-      terminationGracePeriodSeconds: 30

kubernetes.yaml.tmpl

@@ -1,41 +0,0 @@
-apiVersion: apps/v1
-kind: DaemonSet
-metadata:
-  name: skubelb
-  namespace: skubelb
-  labels:
-    k8s-app: skubelb
-spec:
-  selector:
-    matchLabels:
-      name: skubelb
-  template:
-    metadata:
-      labels:
-        name: skubelb
-    spec:
-      tolerations:
-      # these tolerations are to have the daemonset runnable on control plane nodes
-      # remove them if your control plane nodes should not run pods
-      - key: node-role.kubernetes.io/control-plane
-        operator: Exists
-        effect: NoSchedule
-      - key: node-role.kubernetes.io/master
-        operator: Exists
-        effect: NoSchedule
-      containers:
-      - name: skubelb
-        image: us-west4-docker.pkg.dev/nixernetes/images/skubelb-handler:TAG
-        env:
-        - name: NODE_IP
-          valueFrom:
-            fieldRef:
-              fieldPath: status.hostIP
-        command: ["sh", "-c", "./handler -s 10.128.0.2:8888 -l ${NODE_IP}"]
-        resources:
-          limits:
-            memory: 200Mi
-          requests:
-            cpu: 10m
-            memory: 100Mi
-      terminationGracePeriodSeconds: 30

src/main.rs

@@ -1,26 +1,21 @@
-use std::process::Command;
-use std::sync::Arc;
 use std::sync::Mutex;
-use std::thread;
-use std::thread::sleep;
-use std::time::Duration;
 
 use clap::Parser;
 
 use skubelb::Rewriter;
 use skubelb::Server;
 
-use anyhow::{Result, anyhow};
 use env_logger::Env;
 use log::{info, warn};
-use rouille::{Request, Response, router};
+use anyhow::Result;
+use rouille::{router, Request, Response};
 
 /// Implements a HTTP server which allows clients to 'register'
 /// themselves. Their IP address will be used to replace a
 /// needle in a set of config files. This is intended to be
 /// used as a low-cost way of enabling Kubernetes ingress
 /// using nginx running on a machine that has a public port.
-///
+/// 
 /// The needle is expected to be a dummy IP address; something
 /// fairly unique. The goal is to replace nginx files, where
 /// we often repeat lines if we want nginx to load balance between
@@ -33,7 +28,7 @@ struct Args {
     /// and instead N lines (one per replacement) is added to
     /// the output.
     #[arg(short, long)]
-    needle: String,
+    rewrite_string: String,
 
     /// The folder which contains the templates that
     /// will be be searched for the needle.
@@ -41,7 +36,7 @@ struct Args {
     template_dir: String,
 
     /// The symlink that should be updated each time the config changes.
-    ///
+    /// 
     /// Symlinks are used because file updates are not atomic.
     #[arg(short, long)]
     config_symlink: String,
@@ -50,13 +45,8 @@ struct Args {
     #[arg(short, long)]
     workspace_dir: String,
 
-    /// Address to listen for http requests on.
     #[arg(short, long, default_value_t = String::from("0.0.0.0:8080"))]
     listen: String,
-
-    /// Command to reload nginx.
-    #[arg(short, long, default_value_t = String::from("sudo nginx -s reload"))]
-    reload_cmd: String,
 }
 
 fn main() {
@@ -64,92 +54,31 @@ fn main() {
     env_logger::Builder::from_env(Env::default().default_filter_or("info")).init();
     let args = Args::parse();
 
-    let rewriter = Rewriter::new(args.needle);
-    let server_impl = Arc::new(Mutex::new(Server::new(
-        rewriter,
-        args.workspace_dir,
-        args.template_dir,
-        args.config_symlink,
-    )));
-    let reload_command = args.reload_cmd.leak();
-    let reload_command: Vec<&str> = reload_command.split_ascii_whitespace().collect();
-
-    // Start cleanup thread
-    {
-        let server_impl = server_impl.clone();
-        thread::spawn(move || {
-            loop {
-                sleep(Duration::from_secs(30));
-                match cleanup_worker(&server_impl) {
-                    Ok(_) => (),
-                    Err(e) => {
-                        warn!("Error cleaning up handlers {}", e);
-                    }
-                }
-            }
-        });
-    }
+    let rewriter = Rewriter::new(args.rewrite_string);
+    let server_impl = Mutex::new(Server::new(rewriter, args.workspace_dir, args.template_dir, args.config_symlink));
 
     rouille::start_server(args.listen, move |request| {
         info!("Processing request: {:?}", request);
         match handle(request, &server_impl) {
-            Ok((resp, reload)) => {
-                if reload && reload_command.len() > 0 {
-                    let output = Command::new(reload_command[0])
-                        .args(&reload_command[1..])
-                        .output();
-                    match output {
-                        Ok(o) => {
-                            info!("Ran {:?}; exit code: {}", reload_command, o.status);
-                            info!(
-                                "Ran {:?}; stdout: {}",
-                                reload_command,
-                                String::from_utf8_lossy(&o.stdout)
-                            );
-                            info!(
-                                "Ran {:?}; stderr: {}",
-                                reload_command,
-                                String::from_utf8_lossy(&o.stderr)
-                            );
-                        }
-                        Err(e) => {
-                            warn!("Failed to run {:?}: {:?}", reload_command, e);
-                        }
-                    };
-                }
-                resp
-            }
+            Ok(resp) => resp,
             Err(e) => {
                 warn!("{:?}", e);
-                Response {
-                    status_code: 500,
-                    ..Response::empty_400()
-                }
+                Response{status_code: 500, ..Response::empty_400()}
             }
         }
     });
 }
 
-fn handle(request: &Request, server_impl: &Mutex<Server>) -> Result<(Response, bool)> {
+fn handle(request: &Request, server_impl: &Mutex<Server>) -> Result<Response> {
     router!(request,
-        (POST) (/register/{ip: String}) => {
-            let mut server_impl = server_impl.lock().map_err(|_| anyhow!("failed to acquire lock"))?;
-            server_impl.register(request, &ip)?;
-            let must_reload = server_impl.cleanup()?;
-            Ok((Response{status_code: 200, ..Response::empty_204()}, must_reload))
+        (POST) (/register) => {
+            server_impl.lock().unwrap().register(request)?;
+            Ok(Response{status_code: 200, ..Response::empty_204()})
         },
-        (DELETE) (/register/{ip: String}) => {
-            let mut server_impl = server_impl.lock().map_err(|_| anyhow!("failed to acquire lock"))?;
-            server_impl.unregister(request, &ip)?;
-            let must_reload = server_impl.cleanup()?;
-            Ok((Response{status_code: 200, ..Response::empty_204()}, must_reload))
+        (DELETE) (/register) => {
+            server_impl.lock().unwrap().unregister(request)?;
+            Ok(Response{status_code: 200, ..Response::empty_204()})
         },
-        _ => Ok((Response::empty_404(), false)),
+        _ => Ok(Response::empty_404()),
     )
-}
-
-fn cleanup_worker(server_impl: &Mutex<Server>) -> Result<()> {
-    let mut server_impl = server_impl.lock().map_err(|_| anyhow!("failed to acquire lock"))?;
-    server_impl.cleanup()?;
-    Ok(())
-}
+}

src/rewriter.rs

@@ -1,7 +1,6 @@
 use anyhow::Result;
-use std::collections::{HashMap, HashSet};
+use std::collections::HashSet;
 use std::path::Path;
-use std::time::Instant;
 use std::{
     fs::{self, File},
     io::{BufReader, prelude::*},
@@ -10,8 +9,6 @@ use std::{
 pub struct Rewriter {
     source: String,
     replacements: HashSet<String>,
-    // When each replacement should be cleaned up
-    replacement_cleanup: HashMap<String, Instant>,
 }
 
 impl Rewriter {
@@ -19,18 +16,15 @@ impl Rewriter {
         Self {
             source,
             replacements: HashSet::new(),
-            replacement_cleanup: HashMap::default(),
         }
     }
 
-    pub fn add_replacement(&mut self, replacement: String, cleanup: Instant) -> bool {
-        self.replacement_cleanup.insert(replacement.clone(), cleanup);
-        self.replacements.insert(replacement)
+    pub fn add_replacement(&mut self, replacement: String) {
+        self.replacements.insert(replacement);
     }
 
-    pub fn remove_replacement(&mut self, replacement: &str) -> bool {
-        self.replacement_cleanup.remove(replacement);
-        self.replacements.remove(replacement)
+    pub fn remove_replacement(&mut self, replacement: &str) {
+        self.replacements.remove(replacement);
     }
 
     pub fn rewrite_folder(&self, src: &str, dst: &str) -> Result<()> {
@@ -64,75 +58,32 @@ impl Rewriter {
                 // Open 2 files; one to read and translate, and one to write.
                 let source_file = File::open(&src_path)?;
                 let mut dest_file = File::create(&dst_path)?;
-                let mut buff = Vec::with_capacity(2048);
-                let mut reader = BufReader::new(source_file);
+                let reader = BufReader::new(source_file);
 
-                while let Ok(count) = reader.read_until(b'\n', &mut buff) {
-                    if count == 0 {
-                        break;
-                    }
+                for line in reader.lines() {
+                    let line = line?;
                     // If the line is not subject to replacement, copy it and
                     // carry on.
-                    let line = &buff[0..count];
-                    let m = contains(&self.source.as_bytes(), line);
-                    if m.is_none() {
-                        dest_file.write(&line)?;
-                        buff.clear();
+                    if !line.contains(&self.source) {
+                        writeln!(dest_file, "{}", line)?;
                         continue;
                     }
-                    let m = m.unwrap();
-                    let start = &line[0..m.0];
-                    let end = &line[m.1..];
 
                     // Else, repeat the line multiple times, replacing the string
                     // in question
                     for replacement in &replacements {
-                        dest_file.write(start)?;
-                        dest_file.write(replacement.as_bytes())?;
-                        dest_file.write(end)?;
+                        let new_line = line.replace(&self.source, &replacement);
+                        writeln!(dest_file, "{}", new_line)?;
                     }
-                    buff.clear();
                 }
             }
         }
         Ok(())
     }
-
-    pub fn cleanup(&mut self) -> bool {
-        let now = Instant::now();
-        let mut to_remove = vec![];
-        for (name, when) in self.replacement_cleanup.iter() {
-            if when < &now {
-                to_remove.push(name.clone());
-            }
-        }
-        let will_cleanup = to_remove.len() > 0;
-        for name in to_remove {
-            self.remove_replacement(&name);
-        }
-        will_cleanup
-    }
-}
-
-fn contains(needle: &[u8], haystack: &[u8]) -> Option<(usize, usize)> {
-    let mut i = 0;
-    while i + needle.len() <= haystack.len() {
-        let mut j = 0;
-        while i+j < haystack.len() && j < needle.len() && haystack[i+j] == needle[j] {
-            j += 1;
-        }
-        if j == needle.len() {
-            return Some((i, i+j));
-        }
-        i += 1;
-    }
-    None
 }
 
 #[cfg(test)]
 mod tests {
-    use std::time::{Duration, Instant};
-
     use include_directory::{Dir, include_directory};
     use tempdir::TempDir;
 
@@ -146,11 +97,10 @@ mod tests {
         let src = testdata.path().join("testsrc");
         let dst = TempDir::new("").unwrap();
 
-        let now = Instant::now();
         let mut rewriter = Rewriter::new("to_be_replaced".into());
-        rewriter.add_replacement("abc".into(), now.checked_add(Duration::new(60*60*24, 0)).unwrap());
-        rewriter.add_replacement("def".into(), now);
-        rewriter.add_replacement("zyx".into(), now);
+        rewriter.add_replacement("abc".into());
+        rewriter.add_replacement("def".into());
+        rewriter.add_replacement("zyx".into());
         rewriter.remove_replacement("zyx");
         rewriter
             .rewrite_folder(
@@ -163,20 +113,5 @@ mod tests {
         assert!(
             dir_diff::is_different(testdata.path().join("testdst"), dst.path()).unwrap() == false
         );
-
-        // Trigger the cleanup, which should GC abc
-        let dst = TempDir::new("").unwrap();
-        rewriter.cleanup();
-        rewriter
-            .rewrite_folder(
-                src.as_os_str().to_str().unwrap(),
-                dst.path().as_os_str().to_str().unwrap(),
-            )
-            .unwrap();
-
-        // Validate that everything matches
-        assert!(
-            dir_diff::is_different(testdata.path().join("testdst_after_gc"), dst.path()).unwrap() == false
-        );
     }
 }

src/server.rs

@@ -1,13 +1,9 @@
-use std::{
-    fs,
-    path::Path,
-    time::{Duration, Instant},
-};
+use std::{fs, path::Path};
 
-use anyhow::{Context, Result, anyhow};
 use chrono::Utc;
 use log::info;
 use rouille::Request;
+use anyhow::{Context, Result};
 
 use crate::Rewriter;
 
@@ -22,12 +18,7 @@ pub struct Server {
 }
 
 impl Server {
-    pub fn new(
-        rewriter: Rewriter,
-        workspace_dir: String,
-        template_dir: String,
-        config_dir: String,
-    ) -> Self {
+    pub fn new(rewriter: Rewriter, workspace_dir: String, template_dir: String, config_dir: String) -> Self {
         Self {
             rewriter,
             workspace_dir,
@@ -36,30 +27,19 @@ impl Server {
         }
     }
 
-    pub fn cleanup(&mut self) -> Result<bool> {
-        let cleaned_up = self.rewriter.cleanup();
-        if cleaned_up {
-            self.generate_config()?;
-        }
-        Ok(cleaned_up)
-    }
-
-    pub fn register(&mut self, _request: &Request, ip: &str) -> Result<()> {
+    pub fn register(&mut self, request: &Request) -> Result<()> {
+        let ip = request.remote_addr().ip().to_string();
         info!("Registering {} as a handler", ip);
-        let cleanup_time = Instant::now()
-            .checked_add(Duration::from_secs(60))
-            .ok_or(anyhow!("failed to convert time"))?;
-        if self.rewriter.add_replacement(ip.to_string(), cleanup_time) {
-            self.generate_config()?;
-        }
+        self.rewriter.add_replacement(ip);
+        self.generate_config()?;
         Ok(())
     }
 
-    pub fn unregister(&mut self, _request: &Request, ip: &str) -> Result<()> {
+    pub fn unregister(&mut self, request: &Request) -> Result<()> {
+        let ip = request.remote_addr().ip().to_string();
         info!("Deregistering {} as a handler", ip);
-        if self.rewriter.remove_replacement(ip) {
-            self.generate_config()?;
-        }
+        self.rewriter.remove_replacement(&ip);
+        self.generate_config()?;
         Ok(())
     }
 
@@ -71,13 +51,10 @@ impl Server {
         let path = Path::new(&self.workspace_dir).join(&now.format("%Y/%m/%d/%s").to_string());
         let path = path.as_os_str().to_str().unwrap();
         fs::create_dir_all(path).with_context(|| "creating directory")?;
-        self.rewriter
-            .rewrite_folder(&self.template_dir, path)
-            .with_context(|| "generating configs")?;
+        self.rewriter.rewrite_folder(&self.template_dir, path).with_context(|| "generating configs")?;
         // Finally, symlink it to the output folder; only support Linux for now
-        let symlink = Path::new(&self.workspace_dir).join("symlink.tmp");
-        std::os::unix::fs::symlink(path, &symlink).with_context(|| "creating symlink")?;
-        fs::rename(symlink, &self.config_dir).with_context(|| "renaming symlink")?;
+        fs::remove_file(&self.config_dir).with_context(|| "removing old symlink")?;
+        std::os::unix::fs::symlink(path, &self.config_dir).with_context(|| "updating symlink")?;
         Ok(())
     }
-}
+}

src/testdata/testdst_after_gc/hello.txt

@@ -1,4 +0,0 @@
-This is a line
-This is abc line
-
-This is another line

src/testdata/testdst_after_gc/recursive/world.txt

@@ -1,3 +0,0 @@
-This is a abc line.
-
-In a nested directory.

src/testdata/testsrc/hello.txt

@@ -1,4 +1,4 @@
 This is a line
 This is to_be_replaced line
 
-This is another line
+This is another line

src/testdata/testsrc/recursive/world.txt

@@ -1,3 +1,3 @@
 This is a to_be_replaced line.
 
-In a nested directory.
+In a nested directory.