I see a 500 error when I hit my TYPO3 site in ddev.
ddev logs shows me what's going on:
2018/05/10 21:07:38 [error] 354#354: *45 FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught UnexpectedValueException: The current host header value does not match the configured trusted hosts pattern! Check the pattern defined in $GLOBALS['TYPO3_CONF_VARS']['SYS']['trustedHostsPattern'] and adapt it, if you want to allow the current host header 'typo3-master.ddev.local:8000' for your installation. in /var/www/html/typo3/sysext/core/Classes/Utility/GeneralUtility.php:2728
I have ddev v0.18.0 and have run ddev config, and I've confirmed that the AdditionalConfiguration.php contains the generic $GLOBALS['TYPO3_CONF_VARS']['SYS']['trustedHostsPattern'] = '.*';, so that should match anything, right?
TYPO3 v9 seems to not be able to use a trustedHostsPattern that contains a port. You're running on port 8000, for TYPO3 v9 and ddev, please figure out how to get it on port 80. There are troubleshooting instructions on how to figure out what else might be using port 80 at https://ddev.readthedocs.io/en/latest/users/troubleshooting/#unable-listen