Error while updating from Mercurial repository

Overview:

This article describes how to resolve "400 Error: Bad Request while connecting to Mercurial repository".

Symptoms: 

On the administration page you might notice the following error shown in one of your Mercurial projects:

Check for VCS changes completed with errors. jetbrains.vcs.server.api.VcsServiceException: Failed to complete an action for front:front. Failed to collect current revision for front:front. 'hg –config extensions.loadcommandscommandpy=/<Upsource_home_directory>/temp/upsource-analyzer/hg2/load-commands-command.py CMD /<Upsource_home_directory>/temp/upsource-analyzer/hg2/command.args

for command: hg –config ui.interactive=False pull –config extensions.progress= –config progress.format=topic number –config progress.delay=0 –config progress.assume-tty=True http://upsource:******@hg.server' command failed.
stderr: abort: HTTP Error 400: Bad Request

Solution:

This error might be caused by Nginx failing to proxy large request headers. Increasing header size limit in Nginx configs should resolve the issue. More details about the syntax and the default values can be found in the Nginx documentation.