Transitioning To WordPress

Hi all,

I’m transitioning this site from Tumblr to WordPress. I dropped a bunch of posts after 2014 which covered a wide array of App Engine topics – I want to redo those with updated information in 2019, as much has changed with the Google Cloud Platform.

If you have any questions, feel free to contact me using the About page (link above).


Facebook Outbound Email

I’m in the middle of testing an email server on Compute Engine, and I noticed something unusual: apparently Facebook’s outbound email servers insist on using extended SMTP to send email.

With extended SMTP, an email server sends email by opening up a connection and sending the EHLO command. The proper response is either 250 (to indicate success and that extended SMTP support is available) or 550 (the responding server did not understand the command, which is another way of saying that the responding server does not support ESMTP). In case of 550 errors, the usual practice is to fall back to the original SMTP command set and to send a HELO request.

But Facebook’s outbound mail servers seem to only want to connect with ESMTP servers: FB mail servers send a quit command instead of falling back to sending a HELO command.

Another interesting oddity from watching mail logs: Google’s Gmail servers seem to be the only mail servers properly implementing the BDAT command (binary data). I never see any other mail servers attempt to use it.

Error Parsing YAML File: Mapping Values Are Not Allowed Here

An improperly configured YAML file may show the error Error Parsing YAML File: Mapping Values Are Not Allowed Here . This error is demonstrated below:

Here is an example YAML file that causes this error:

#Error happens at line 7 below, even though the incorrect lines are above.
- url: /example

Even though the YAML parser reports the error at line 7, the actual incorrect lines are above that point: lines 1 – 5 are missing the space character between the colon and the value. If you encounter this error, make sure that the key: value pairs are separated by 1 colon and 1 space character, as shown below:

application: application-id

IOException: tmpFile.renameTo Failed

On rare occasions, the Google App Engine dev server displays the following error:

The important part of the error is this text: tmpFile.renameTo(classfile) failed

This exception crops up whenever an app file (in this case a JSP file) is currently being accessed by another program. If you see this exception, double check to ensure that the named file isn’t being accessed by another program.

If this error persists, close down and reopen Eclipse and the development app server – the file may have been left open from a previous run.

Whitelisted PHP Extensions

Google App Engine permits only specific whitelisted extensions to be used within PHP applications. If you use a non-whitelisted extension, you’ll see the below error:

The [php_extension_name] extension is missing. 
Please check your PHP configuration.

If you need a certain extension for your PHP application, ensure that it’s enabled in GAE: check the official list at . If your preferred extension is not listed, you can also try searching for a pure-PHP implementation (Pure PHP extensions can always be uploaded as part of an application; C based extensions must be whitelisted.)

If you need an extension not listed in the above link, you can request it via the App Engine issues tracker. For example, here’s a feature request for the ImageMagick extension:

Downloading The Contents Of A MediaWiki Install

Here’s an useful wget command: it downloads a static copy of a MediaWiki installation while skipping unimportant pages, such as the talk sections. Downloading large sites can take a long time, so the nohupinstruction lets this command continue even when the user exits from the shell.

nohup wget --recursive --page-requisites --html-extension \
    --convert-links --no-parent -R "*Special*" -R "*action=*" \
    -R "*printable=*" -R "*title=Talk:*" \

You can use this command to archive old wiki installs, or keep a local copy for quick reference.

App Engine System Status

The App Engine system status console is located at . It’s a good idea to keep this page bookmarked to monitor GAE’s performance.

Here’s how the status page looks like when everything is running well:

Here’s an example of how performance issues are reported:

The Term (Domain) Is Not Allowed

While configuring a domain within Google Apps, you may see the error message “ The Term [Domain Name] Is Not Allowed ”:

This error can come up due to several problems. The most likely issue is that the domain has been configured as an independent domain, rather than as an alias domain. A quick fix to this issue is to delete this domain from Google Apps, and then to re-add it. When the prompt comes up to select independent domain versus alias domain, select the alias domain option.

Slashdot Downtime Notices

I like to collect samples of downtime notices and error messages from popular websites; it’s always fascinating to see how sites handle messaging on technical issues.

Here’s an example downtime notice from Slashdot:

Here is the message in context: