HTTP 502 response

If you receive HTTP 502 responses from your site, it means that your site is running out of workers. Here are the typical causes:

  • The amount of traffic coming to your site exceeds the processing power of your application.
  • Certain code path(s) in your application are too slow.

If you are using our PHP application containers (e.g. type: php:7.1), you can use this example CLI command to find the top 20 slowest requests in the last hour.

platform ssh "grep $(date +%Y-%m-%dT%H --date='-1 hours') /var/log/php.access.log | sort -k 4 -r -n | head -20"

If you see that the processing time of certain requests is slow (e.g. taking more than 1000ms), you may wish to consider using a profiler like Blackfire to debug the performance issue.

Otherwise, you may check if the following options are applicable:

  • Find the most visited pages and see if they can be cached and/or put behind a CDN. You may refer to how caching works.
  • Upgrade your subscription on to get more computing resources. To do so, log into your account and edit the project.

MySQL lock wait timeout

If you receive MySQL error messages like this:

SQLSTATE[HY000]: General error: 1205 Lock wait timeout exceeded;

This means a process running in your application acquired a lock from MySQL for a long period of time. That is typically caused by one of the following:

  • There are multiple places acquiring locks in different order. For example, code path 1 first locks record A and then locks record B. Code path 2, in contrast, first locks record B and then locks record A.
  • There is a long running background process executed by your application that holds the lock until it ends.

If you're using MariaDB 10.0, you can use SQL query SHOW FULL PROCESSLIST \G to list DB queries waiting for locks. Find output like the following, and start debugging.

< skipped >
Command: Query
Time: ...
State: Waiting for table metadata lock
Info: SELECT ...
< skipped >

To find active background processes, run ps aufx on your application container.

Also, please make sure that locks are acquired in a pre-defined order and released as soon as possible.

"Read-only file system" error

Everything will be read-only, except the writable mounts you declare. Writable mounts are there for your data: for file uploads, logs and temporary files. Not for your code. In order to change code on you have to go through Git.

This is what gives you all of the benefits of having repeatable deployments, consistent backups, traceability, and the magically fast creation of new staging/dev environments.

In, you cannot just "hack production". It is a constraint, but it is a good constraint.

During the build phase of your application, the main filesystem is writable. So you can do whatever you want (e.g. compile code or generate anything you need). But during and after the deploy phase, the main filesystem will be read-only.

"File not found" in Drupal

If you see a bare "File not found" error when accessing your Drupal site with a browser, this means that you've pushed your code as a vanilla project but no index.php has been found.

Make sure your repository contains an index.php file in the web location root, or that your Drush make files are properly named.

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