Dependencies are not necessarily packaged for all architectures. In some cases
(such as aiohttp, and others, on ARM) pip will attempt to compile the
dependency from scratch. Since switching to multi-stage builds, we have been
installing these without a compiler present which caused the build to fail on
ARM architectures.
This commit temporarily installs build-essential packages while running pip,
then removes them again afterwards.
This is more robust, as it indicates the request was successfully
authenticated and processed, but that there is no data to export. This is
different from the URL not existing (which would also happen if the module was
unavailable, which should be a notable error instead).
Found in production. Yes really. Due to some borked LXC integration, my
snikket host reports
```
MemTotal: 9007199254740991 kB
MemFree: 9007199254690591 kB
MemAvailable: 9007199254690591 kB
```
That is more than 1024 TiB, so it tries to go further up in the scale,
which then causes a Guru Meditation because of the uncaught IndexError.
Previously, the multi-stage build increased the image size by about 30
MiB (163MiB -> 191MiB). Dropping the caches reduces the image size down
to 159MiB, leading to a net improvement of 4 MiB.
Currently the Dockerfile has a single RUN directive with all the needed
commands in it. This optimizes for image size by not creating too many
"layers" (which are only additive). However it means the result that gets
cached can basically never be reused, because any change to the source code
will need to execute the whole RUN block again.
This commit switches to a docker "multi-stage" build, where we have a build
image that is separate from the final one that gets published. The build
image can be cached locally, and size is no longer a significant concern.
This approach allows the single RUN command to be split up into multiple RUN
commands that only execute when strictly needed (i.e. when their result
is not cached locally).
This drastically improves the build time when rebuilding the image after
a simple code change, because the build image doesn't have to install all
the apt packages, for example. This leads to a nicer developer experience
when using docker locally for development and testing.
wtforms 3.0 is incompatible with our code. A separate issue will be
filed to address the incompatibilities, but this should be enough to get
working images out of it.
With 3.x, we're seeing:
```
File "/home/horazont/Projects/python/snikket-web-portal/snikket_web/main.py", line 35, in LoginForm
address = wtforms.TextField(
AttributeError: module 'wtforms' has no attribute 'TextField'
```
and the portal fails to start.
