Why Your Dokploy Next.js VPS Deploy Fails: 3 Core Issues

Introduction: The Dokploy Dream vs. Deployment Reality

You've found the perfect self-hosted PaaS solution in Dokploy. You've spun up a fresh VPS, pointed your domain, and you're ready to deploy your slick Next.js application. It promises a Heroku-like experience on your own terms. You hit 'Deploy', watch the logs scroll by with anticipation, and then... failure. A cryptic error message, a 502 Bad Gateway, or just a build process that hangs indefinitely. The dream of simple, self-hosted deployment quickly turns into a frustrating debugging session.

If this sounds familiar, you're not alone. While Dokploy significantly simplifies containerized deployments, the interaction between its build process, your Next.js application's specific needs, and the limitations of a typical VPS creates a common set of failure points. The good news is that these failures almost always trace back to one of three core issues.

In this guide, we'll dissect these three problems, providing clear explanations and actionable solutions to get your Next.js app running smoothly on your Dokploy-powered VPS. We'll move beyond generic advice and dive into the specific configurations that trip up so many developers.

Issue #1: Misconfigured Build Settings and Environment Variables

The most frequent culprit behind a failed Dokploy deployment is a mismatch between what your Next.js application expects and what Dokploy provides. This often manifests in how environment variables and build commands are handled.

The NEXT_PUBLIC_ Prefix Pitfall

Next.js has a strict system for managing environment variables to prevent accidentally leaking server-side secrets to the client. This is a fantastic security feature, but it's a common source of deployment errors.

• Server-Side Variables: These are secrets like DATABASE_URL, API_SECRET_KEY, or REDIS_PASSWORD. They are only accessible in server environments (like `getServerSideProps` or API routes) and should never be prefixed with NEXT_PUBLIC_.
• Client-Side Variables: These are variables that need to be accessible in the browser, such as NEXT_PUBLIC_API_URL or NEXT_PUBLIC_GOOGLE_ANALYTICS_ID. They must be prefixed with NEXT_PUBLIC_.

The Failure Point: During the next build process, which Dokploy runs inside a Docker container, Next.js replaces all instances of process.env.NEXT_PUBLIC_... with their actual values. If your code tries to access a non-prefixed variable on the client-side, it will be undefined, leading to build failures or runtime errors. Conversely, if you define a server-side secret in the Dokploy UI but your code doesn't access it correctly (or you forget to add it entirely), your application will fail when it tries to connect to a database or other service.

The Solution: Double-check every environment variable in your code. Audit your .env.local file and ensure every variable is correctly categorized. Then, meticulously enter them into the Dokploy application's 'Environment Variables' section. Remember, variables for the build process and the final running application are both managed here.

Missing or Incorrect 'build' and 'start' Commands

Dokploy is smart, but it's not a mind reader. It relies on standard conventions found in your project's package.json file to build and run your application. For a Next.js app, it specifically looks for two scripts:

1. "build": "next build": This command compiles your application for production.
2. "start": "next start": This command starts the production server. By default, it runs on port 3000.

The Failure Point: If these scripts are missing from your package.json, or if they've been modified (e.g., "dev": "next dev" is present but start is not), Dokploy's build pack won't know what to do. The build might fail immediately with an error like "script 'build' not found." Even if the build succeeds (perhaps you have a custom Dockerfile), if the start command is wrong, the container will launch and then immediately exit, resulting in a 502 error.

The Solution: Ensure your package.json contains the standard scripts. A typical Next.js scripts section should look like this:

"scripts": {
  "dev": "next dev",
  "build": "next build",
  "start": "next start",
  "lint": "next lint"
}

In the Dokploy application settings, under the 'Build' tab, you can typically leave the 'Build Command' and 'Start Command' fields blank if your package.json is set up correctly, as Dokploy's buildpacks will infer them. However, if you have a custom setup, this is where you would explicitly define them.

Issue #2: Dockerfile Discrepancies and Port Conflicts

When you move to a container-based platform like Dokploy, you're introducing Docker into the mix. This powerful tool brings its own set of rules, particularly concerning ports and the build environment.

The Default Port Problem: 3000 vs. The World

By default, a production Next.js application started with next start listens on port 3000. Dokploy needs to know this so it can map an external port (like 80/443 for web traffic) to the internal port of your running container.

The Failure Point: A deployment can succeed, the logs might even say 'ready - started server on 0.0.0.0:3000', but you still see a 502 Bad Gateway. This happens when there's a mismatch between the port your app is listening on and the port Dokploy thinks your app is listening on.

The Solution:

1. Dokploy UI: In your application's 'General' settings, find the 'Port' configuration. Ensure this is set to 3000 (or whatever port your Next.js app is configured to use).
2. Dockerfile (if using one): If you're providing a custom Dockerfile, make sure you include the EXPOSE 3000 instruction. This doesn't actually publish the port, but it serves as important metadata for Dokploy and anyone else inspecting the image.
3. Custom Port: If you need to run on a different port, you can change your package.json start script to "start": "next start -p 8080". If you do this, you must update the port in the Dokploy UI to 8080 to match.

Inconsistent Node.js Versions

You developed your app locally using Node.js v20.5.0. But the Docker image Dokploy is using to build your app is based on Node.js v18.17.0. This slight difference can be a source of insidious build failures.

The Failure Point: Dependencies, especially those with native C++ bindings, can be highly sensitive to the Node.js version. A package that installs perfectly on your machine might fail to compile inside the build container. This can lead to errors that seem unrelated to Node itself, sending you on a wild goose chase debugging a specific package when the root cause is the environment.

The Solution:

• Use Dokploy's Buildpacks: If you're not using a custom Dockerfile, check the Dokploy documentation or settings to see which Node.js version its buildpack uses. You can often specify a version by including an engines field in your package.json:
  "engines": { "node": ">=18.17.0" }
• Use a Custom Dockerfile: This is the most reliable method. Explicitly define the Node.js version in your Dockerfile to match your development environment. This ensures consistency everywhere.
  FROM node:18-alpine AS base
• Use .nvmrc: Create a .nvmrc file in your project root containing your desired Node version (e.g., v18.17.0). This helps you and your team stay on the same version locally and can be referenced in build scripts.

Issue #3: VPS Resource Constraints and File Permissions

Finally, the problem might not be with your code or configuration, but with the server itself. A budget-friendly VPS is great for hosting, but the next build process can be surprisingly demanding.

The Silent Killer: RAM Exhaustion During Build

The Failure Point: You start a deployment, and the build log runs for a while, then suddenly stops with a generic 'Killed' message or a timeout error. This is a classic symptom of your server running out of memory (RAM). The Linux kernel's Out-Of-Memory (OOM) Killer steps in and terminates the most memory-hungry process—in this case, your build.

This is especially common on VPS instances with 1GB or 2GB of RAM, as a complex Next.js application with many pages, image optimization, and heavy dependencies can easily consume more memory than is available during the static generation and compilation phase.

The Solution: Create a Swap File. A swap file acts as overflow virtual memory on your server's hard drive. While slower than physical RAM, it provides the necessary buffer to get through a demanding build process.

To create a 2GB swap file on your Ubuntu/Debian VPS, SSH into your server and run these commands:

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab
sudo sysctl vm.swappiness=10

This one-time setup can permanently solve build-related memory issues.

'Permission Denied': The Digital Gatekeeper

The Failure Point: The build fails very early with an error like EACCES: permission denied. This indicates that the user running the build process inside the Docker container does not have the necessary permissions to read your project files or write to the output directory (.next).

This can happen if you manually copied files to your VPS as the root user, but Dokploy's agent (or the Docker user) is running as a non-root user.

The Solution: Fix Directory Ownership. SSH into your VPS and navigate to the directory where Dokploy stores your applications (often in /var/lib/dokploy/apps/... or a directory you've configured). Find your project's source code directory and ensure the ownership is correct. A common fix is to change the ownership to the user that the Dokploy agent runs as, or to a more generic user like www-data if applicable. Use the chown command:

# Example: Change ownership to the 'dokploy' user recursively
sudo chown -R dokploy:dokploy /path/to/your/app/source

You may need to investigate which user Dokploy is operating as on your specific system. Checking the permissions of a successfully deployed app's directory can provide a clue.

Conclusion: From Failed Deploy to Flawless Flow

A failed deployment is a roadblock, not a dead end. By systematically investigating these three core areas—configuration, containerization, and server resources—you can overcome nearly any issue you encounter when deploying a Next.js application with Dokploy. The path from a failed build log to a live, running application is often just one small, targeted fix away.

Start with the most common culprit: your environment variables and package.json scripts. If those are solid, move on to your port and Node.js version alignment. Finally, if the build process itself is failing on a lean VPS, a swap file is your best friend. Once you conquer these initial hurdles, you'll unlock the true power of Dokploy, enjoying fast, repeatable, and stress-free deployments for all your future projects.