Fix: Playwright MCP Chrome Profile Lock In Jenkins

by Kenji Nakamura 51 views

Hey guys, let's dive into troubleshooting a tricky issue we've encountered with Playwright MCP and Jenkins on Windows. We're seeing a consistent failure when running tasks via Jenkins that work perfectly fine when executed directly through PyCharm. This article is all about breaking down the problem, understanding the environment, and exploring potential solutions. So, buckle up, and let's get started!

Issue Encountered

The Problem: Chrome Profile Lock

Our main headache is this error message: "Error: Browser is already in use for C:\Users\vagrant\AppData\Local\ms-playwright\mcp-chrome-profile, use --isolated to run multiple instances of the same browser". This pops up when running a Jenkins job that uses the mcp-use library and LangChain integration with Playwright MCP. The weird part? It only happens with Chrome. Firefox, WebKit, and Edge are playing nice.

Let's break it down further. When running automation tasks, it is crucial that your browser profiles are managed correctly to avoid conflicts and ensure stability. This error message indicates that the Playwright MCP (Managed Chrome Profile) system believes another process is already using the specified Chrome profile, which prevents the new instance from launching. The core of the issue lies in how Playwright MCP handles persistent profiles across different execution contexts, particularly within the Jenkins environment. The error suggests a lock or a flag is not being released correctly when the browser instance closes, or that the profile directory is not being accessed in a way that is compatible with concurrent executions.

Understanding the error message is the first step, but the real challenge is figuring out why this is happening specifically in Jenkins and not when running the same code locally in PyCharm. This discrepancy points to environmental differences between the two execution contexts, such as user permissions, process isolation, or how Jenkins manages temporary files and directories. For instance, Jenkins jobs often run under a different user account than the one used for interactive sessions, which can lead to file access conflicts if the profile directory isn't configured for shared access. Moreover, Jenkins' workspace management might inadvertently create conditions where the lock files used by Playwright to prevent concurrent profile access are not correctly handled. These factors combine to create a situation where the browser appears to be in use even when it isn't, triggering the error and halting the test execution. To effectively troubleshoot this issue, a methodical approach is necessary, focusing on isolating the specific environmental factors that cause the profile lock.

Here's the gist:

  • We can't start the browser in Jenkins due to this error:
    Error: Browser is already in use for C:\Users\vagrant\AppData\Local\ms-playwright\mcp-chrome-profile, use --isolated to run multiple instances of the same browser

Environment Details

To give you the full picture, here's our setup:

  • OS: Windows Server (where the Jenkins agent lives).
  • Execution Contexts:
    • âś… PyCharm (direct execution) - Works
    • ❌ Jenkins Job (same machine) - Fails
  • MCP Tool: @playwright/mcp@latest
  • Profile Path: C:\Users\vagrant\AppData\Local\ms-playwright\mcp-chrome-profile

A crucial point: We've confirmed that no other Playwright or MCP processes are running when the Jenkins job kicks off. This eliminates the most obvious cause of the error, making the situation more perplexing and highlighting the need to dig deeper into the specific dynamics of the Jenkins environment. When dealing with automation in CI/CD systems like Jenkins, it is not uncommon to encounter issues that are not reproducible in local development environments due to the differences in how resources are managed and processes are executed. Jenkins jobs often run in isolated environments or under different user accounts, which can affect file system access, environment variables, and process isolation. In this context, the fact that no other Playwright processes are running does not necessarily mean there aren't residual locks or orphaned processes that Playwright might be detecting. For example, a previous job that crashed or was abruptly terminated might have left behind a lock file or a lingering process that prevents subsequent jobs from using the same profile. Understanding these nuances is essential when troubleshooting profile lock issues in Jenkins, as the root cause often lies in the subtle interactions between the automation tool, the CI/CD system, and the underlying operating system. Thus, a comprehensive investigation requires examining not only the current state of the system but also the potential remnants of previous executions and the specific configurations of the Jenkins job.

Expected vs. Actual Behavior

  • Expected: Playwright MCP should reuse the default profile (mcp-chrome-profile) whether it's run via Jenkins or PyCharm, as long as no other browser instance is using it.
  • Actual: When launched via Jenkins, Playwright MCP incorrectly thinks the profile is already in use, causing the browser to fail to start.

This discrepancy between expected and actual behavior underscores the core challenge: understanding why Jenkins triggers this false positive. It suggests that there's something specific about the Jenkins environment—perhaps the way it handles file locking, user permissions, or process isolation—that's causing Playwright MCP to misinterpret the profile's status. The fact that the same setup works perfectly for other browsers (Firefox, WebKit, and Edge) further narrows down the problem to Chrome and its interaction with Playwright MCP within the Jenkins context. This could be related to how Chrome's profile management differs from other browsers or how Playwright MCP handles Chrome-specific features. The implication is that the solution might involve adjusting either the Jenkins configuration, the Playwright MCP settings, or even the way Chrome is invoked within the Jenkins job. To pinpoint the exact cause, we need to systematically analyze the differences between the Jenkins and PyCharm environments, focusing on factors that could affect file access, process management, and inter-process communication. This might involve examining environment variables, user permissions, file locking mechanisms, and any other configurations that could potentially influence how Playwright MCP interacts with Chrome within the Jenkins environment.

Key Observation

Remember, at the time of the Jenkins job, there are no other playwright-mcp processes running on the machine.

Diving Deeper: Potential Causes and Solutions

Okay, guys, let's roll up our sleeves and get into the nitty-gritty. We've got a solid understanding of the problem, so now it's time to brainstorm potential causes and solutions. Given that the issue is specific to Chrome in Jenkins, we need to consider factors that might affect Chrome's behavior in that environment.

1. Lock Files and Process Isolation

Understanding Lock Files: One of the first things to consider when troubleshooting browser profile lock issues is how the browser and the automation tool manage lock files. Lock files are a mechanism used by applications to prevent multiple instances from accessing the same resources simultaneously, which is especially critical for browser profiles to avoid data corruption and ensure consistency. When a browser instance starts, it often creates a lock file within the profile directory to signal that the profile is in use. If another instance attempts to use the same profile while the lock file exists, it will be denied access, leading to the