Changes to nginx @maintenance handler

[stick]

previous configuration would not display maintenance page if omero.web
wasn't running. This was likely due to the request being passed to the
@proxy_to_app named location and the configuration not being inherited
into that stanza.

This commit moves the error_page directive up to the server container
where possible or duplicates the directive into the named location
directive otherwise.

Additionally the return code is set to 502 to avoid situations where
returning the maintenance page causes a 200 return code and confusing
monitoring systems. (502 is always 502 with the current configuration.

[sbesson]

Thanks for opening this @stick. The remaining failing test is the following which makes assumptions about nginx.conf vs nginx-location.conf

omero-web/test/unit/test_web.py

Lines 477 to 507 in 9e0d870

	def testNginxLocationComment(self):
	"""
	Check the example comment in nginx-location matches the recommended
	nginx configuration
	"""
	def clean(refname):
	fn = path(__file__).dirname() / 'reference_templates' / refname
	out = []
	with open(fn) as f:
	for line in f:
	if re.match(r'##\s*\w', line):
	out.append(line[2:].strip())
	elif re.match(r'[^#]\s*\w', line):
	out.append(line.strip())
	return out
	diffs = list(unified_diff(
	clean('nginx.conf'), clean('nginx-location.conf'), n=0))
	assert diffs == [
	'--- \n',
	'+++ \n',
	'@@ -1,2 +0,0 @@\n',
	'-upstream omeroweb {',
	'-server 127.0.0.1:4080 fail_timeout=0;',
	'@@ -7,0 +6 @@\n',
	'+include /opt/omero/web/omero-web-location.include;',
	'@@ -19 +18 @@\n',
	'-proxy_pass http://omeroweb;',
	'+proxy_pass http://127.0.0.1:4080;'
	]

Given the divergence introduced in this PR between these two configuration files, is it worth trying to update the test or should this PR drop it so that we can review it @manics ?

[manics]

I'm happy to see us remove nginx-location completely in the next breaking release.
omero.web.nginx_server_extra_config provides a lot of flexibility.

[imagesc-bot]

This pull request has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/omero-web-maintenance-page/38552/2

[joshmoore]

Re-opening with #174 in.

[joshmoore]

Still failing with:

E       AssertionError: assert ['--- \n', '+...+6 @@\n', ...] == ['--- \n', '+...+6 @@\n', ...]
2113E         At index 5 diff: '@@ -8 +6 @@\n' != '@@ -7,0 +6 @@\n'
2114E         Left contains 5 more items, first extra item: '@@ -20 +19 @@\n'
2115E         Use -v to get the full diff

Perhaps the changes from the uncommented run need adding?

cc: @stick @manics

[snoopycrimecop]

Conflicting PR. Removed from build OMERO-python-superbuild-push#2. See the console output for more details.
Possible conflicts:

• Upstream changes
  • test/unit/test_web.py

--conflicts