Trying to get latest flexget up and runnng using Docker for Synology

Hi,

Im trying to use this guide to setup Docker and Flexget on Synology Nas.

https://flexget.com/InstallWizard/SynologyNAS/Docker

First step failed to create the flexget user as per the Dockerscrip, but i worked around that by specifying the docker UID in the dockerfile script.
However after that it fails on other steps:

ash-4.3# docker build --build-arg DOCKER_UID=1027 -t flexget:3.1.45 .
Sending build context to Docker daemon  4.096kB
Step 1/10 : FROM     python:3.6-alpine
 ---> 5e7f84829665
Step 2/10 : RUN      adduser -D -u 1027 flexget
 ---> Running in ef2a4b67f9c3
Removing intermediate container ef2a4b67f9c3
 ---> b678cc32cb69
Step 3/10 : WORKDIR  /home/flexget
 ---> Running in b3d91e3bf294
Removing intermediate container b3d91e3bf294
 ---> bb893802f87a
Step 4/10 : VOLUME   /home/flexget/.flexget
 ---> Running in 9b4730733669
Removing intermediate container 9b4730733669
 ---> 16830b05cf7d
Step 5/10 : VOLUME   /home/flexget/torrents
 ---> Running in 8b28bd6af7b7
Removing intermediate container 8b28bd6af7b7
 ---> 85bb7d75d5cf
Step 6/10 : RUN      pip3 install -U pip && pip3 install flexget
 ---> Running in a85b6613ffba
Requirement already up-to-date: pip in /usr/local/lib/python3.6/site-packages (20.0.2)
Collecting flexget
  Downloading FlexGet-3.1.45-py2.py3-none-any.whl (8.9 MB)
Collecting markupsafe==1.1.1
  Downloading MarkupSafe-1.1.1.tar.gz (19 kB)
Collecting more-itertools==7.2.0
  Downloading more_itertools-7.2.0-py3-none-any.whl (57 kB)
Collecting zc.lockfile==2.0
  Downloading zc.lockfile-2.0-py2.py3-none-any.whl (9.7 kB)
Collecting itsdangerous==0.24
  Downloading itsdangerous-0.24.tar.gz (46 kB)
Collecting cheroot==8.2.1
  Downloading cheroot-8.2.1-py2.py3-none-any.whl (79 kB)
Collecting loguru==0.4.1
  Downloading loguru-0.4.1-py3-none-any.whl (54 kB)
Collecting pytz==2017.2
  Downloading pytz-2017.2-py2.py3-none-any.whl (484 kB)
Collecting jinja2==2.10.1
  Downloading Jinja2-2.10.1-py2.py3-none-any.whl (124 kB)
Collecting aniso8601==1.2.1
  Downloading aniso8601-1.2.1.tar.gz (62 kB)
Collecting werkzeug==0.15.6
  Downloading Werkzeug-0.15.6-py2.py3-none-any.whl (328 kB)
Collecting zxcvbn-python==4.4.15
  Downloading zxcvbn-python-4.4.15.tar.gz (405 kB)
Collecting flask-restplus==0.10.1
  Downloading flask_restplus-0.10.1-py2.py3-none-any.whl (1.0 MB)
Collecting plumbum==1.6.3
  Downloading plumbum-1.6.3-py2.py3-none-any.whl (99 kB)
Collecting progressbar==2.5
  Downloading progressbar-2.5.tar.gz (10 kB)
Collecting flask-login==0.4.0
  Downloading Flask_Login-0.4.0-py2.py3-none-any.whl (15 kB)
Collecting idna==2.8
  Downloading idna-2.8-py2.py3-none-any.whl (58 kB)
Collecting sqlalchemy==1.3.11
  Downloading SQLAlchemy-1.3.11.tar.gz (6.0 MB)
Collecting colorclass==2.2.0
  Downloading colorclass-2.2.0.tar.gz (17 kB)
Collecting soupsieve==1.9.5
  Downloading soupsieve-1.9.5-py2.py3-none-any.whl (33 kB)
Collecting flask-cors==3.0.2
  Downloading Flask_Cors-3.0.2-py2.py3-none-any.whl (15 kB)
Collecting rebulk==2.0.0
  Downloading rebulk-2.0.0.tar.gz (257 kB)
Collecting click==6.7
  Downloading click-6.7-py2.py3-none-any.whl (71 kB)
Collecting flask-restful==0.3.6
  Downloading Flask_RESTful-0.3.6-py2.py3-none-any.whl (25 kB)
Collecting python-dateutil==2.6.1
  Downloading python_dateutil-2.6.1-py2.py3-none-any.whl (194 kB)
Collecting terminaltables==3.1.0
  Downloading terminaltables-3.1.0.tar.gz (12 kB)
Collecting feedparser==5.2.1
  Downloading feedparser-5.2.1.tar.bz2 (192 kB)
Collecting pyparsing==2.2.0
  Downloading pyparsing-2.2.0-py2.py3-none-any.whl (56 kB)
Collecting webencodings==0.5.1
  Downloading webencodings-0.5.1-py2.py3-none-any.whl (11 kB)
Collecting html5lib==0.999999999
  Downloading html5lib-0.999999999-py2.py3-none-any.whl (112 kB)
Collecting jaraco.functools==2.0
  Downloading jaraco.functools-2.0-py2.py3-none-any.whl (6.7 kB)
Collecting requests==2.21.0
  Downloading requests-2.21.0-py2.py3-none-any.whl (57 kB)
Collecting cherrypy==18.4.0
  Downloading CherryPy-18.4.0-py2.py3-none-any.whl (418 kB)
Collecting six==1.13.0
  Downloading six-1.13.0-py2.py3-none-any.whl (10 kB)
Collecting flask-compress==1.4.0
  Downloading Flask-Compress-1.4.0.tar.gz (6.0 kB)
Collecting rpyc==4.0.1
  Downloading rpyc-4.0.1.tar.gz (54 kB)
Collecting pillow==7.0.0
  Downloading Pillow-7.0.0.tar.gz (38.2 MB)
Collecting pynzb==0.1.0
  Downloading pynzb-0.1.0.tar.gz (5.6 kB)
Collecting guessit==3.1.0
  Downloading guessit-3.1.0.tar.gz (144 kB)
Collecting beautifulsoup4==4.8.2
  Downloading beautifulsoup4-4.8.2-py3-none-any.whl (106 kB)
Collecting babelfish==0.5.5
  Downloading babelfish-0.5.5.tar.gz (90 kB)
Collecting apscheduler==3.5.0
  Downloading APScheduler-3.5.0-py2.py3-none-any.whl (60 kB)
Collecting portend==2.6
  Downloading portend-2.6-py2.py3-none-any.whl (5.1 kB)
Collecting pyyaml==5.1.2
  Downloading PyYAML-5.1.2.tar.gz (265 kB)
Collecting tempora==1.8
  Downloading tempora-1.8-py2.py3-none-any.whl (11 kB)
Collecting urllib3==1.24.2
  Downloading urllib3-1.24.2-py2.py3-none-any.whl (131 kB)
Collecting chardet==3.0.3
  Downloading chardet-3.0.3-py2.py3-none-any.whl (133 kB)
Collecting pyrss2gen==1.1
  Downloading PyRSS2Gen-1.1.tar.gz (6.9 kB)
Collecting pystray==0.15.0
  Downloading pystray-0.15.0-py2.py3-none-any.whl (43 kB)
Collecting certifi==2017.4.17
  Downloading certifi-2017.4.17-py2.py3-none-any.whl (375 kB)
Collecting tzlocal==1.4
  Downloading tzlocal-1.4.tar.gz (15 kB)
Collecting flask==1.0.2
  Downloading Flask-1.0.2-py2.py3-none-any.whl (91 kB)
Collecting jsonschema==2.6.0
  Downloading jsonschema-2.6.0-py2.py3-none-any.whl (39 kB)
Requirement already satisfied: setuptools in /usr/local/lib/python3.6/site-packages (from zc.lockfile==2.0->flexget) (46.1.1)
Collecting aiocontextvars>=0.2.0; python_version < "3.7"
  Downloading aiocontextvars-0.2.2-py2.py3-none-any.whl (4.9 kB)
Collecting python-xlib>=0.17; sys_platform == "linux"
  Downloading python_xlib-0.26-py2.py3-none-any.whl (174 kB)
Collecting contextvars==2.4; python_version < "3.7"
  Downloading contextvars-2.4.tar.gz (9.6 kB)
Collecting immutables>=0.9
  Downloading immutables-0.11.tar.gz (38 kB)
Building wheels for collected packages: markupsafe, itsdangerous, aniso8601, zxcvbn-python, progressbar, sqlalchemy, colorclass, rebulk, terminaltables, feedparser, flask-compress, rpyc, pillow, pynzb, guessit, babelfish, pyyaml, pyrss2gen, tzlocal, contextvars, immutables
  Building wheel for markupsafe (setup.py): started
  Building wheel for markupsafe (setup.py): finished with status 'done'
  Created wheel for markupsafe: filename=MarkupSafe-1.1.1-py3-none-any.whl size=12629 sha256=46ecd4eed06d8478251898fcda008eb0e6538b29dcb07388b0fd886b8b21b2ad
  Stored in directory: /root/.cache/pip/wheels/ca/85/2f/4c3a8ca6fb5eec7b43ec1e5666c7274dcdb86d6c32231aaa9d
  Building wheel for itsdangerous (setup.py): started
  Building wheel for itsdangerous (setup.py): finished with status 'done'
  Created wheel for itsdangerous: filename=itsdangerous-0.24-py3-none-any.whl size=10621 sha256=05be1696e7b83dd71988e860b30ef8bc90194b339577855e1a21fd2dacc055d9
  Stored in directory: /root/.cache/pip/wheels/87/c5/5a/ec57bae8cc6dc7933ea260ae3170fd858bec5673131c289a95
  Building wheel for aniso8601 (setup.py): started
  Building wheel for aniso8601 (setup.py): finished with status 'done'
  Created wheel for aniso8601: filename=aniso8601-1.2.1-py3-none-any.whl size=16491 sha256=9686d902e85736d3c6c7367cc81110ddfcf11ded53ec87eecb842243abb5709b
  Stored in directory: /root/.cache/pip/wheels/f7/13/5b/22722aa8363dec3035074592194af7fbd02d9dbb40eb23d4c6
  Building wheel for zxcvbn-python (setup.py): started
  Building wheel for zxcvbn-python (setup.py): finished with status 'done'
  Created wheel for zxcvbn-python: filename=zxcvbn_python-4.4.15-py3-none-any.whl size=405290 sha256=2cf3dc2f183a971adbab6426678d5f7f5d7144a83b2eae334d919e78fbe26dd7
  Stored in directory: /root/.cache/pip/wheels/e2/cd/6e/7d614277d63a148f3441e0480fbb1424c1778c036d93cf8640
  Building wheel for progressbar (setup.py): started
  Building wheel for progressbar (setup.py): finished with status 'done'
  Created wheel for progressbar: filename=progressbar-2.5-py3-none-any.whl size=12074 sha256=9daa12b8ab3688ca227e7a60727200e747a07310ece896dc211393c945fb3158
  Stored in directory: /root/.cache/pip/wheels/bc/13/93/a9bf6b3d3966e4af014b0dbef027fdea47393faf47e990349f
  Building wheel for sqlalchemy (setup.py): started
  Building wheel for sqlalchemy (setup.py): finished with status 'done'
  Created wheel for sqlalchemy: filename=SQLAlchemy-1.3.11-cp36-cp36m-linux_x86_64.whl size=1164862 sha256=dd430e2af78bca4904dd1eeaa1e9561d86135176424d23abd53cbc19fc2489b2
  Stored in directory: /root/.cache/pip/wheels/f0/ee/f8/0fcdbfbd6ede87f2a8872888514cbd6892db6d72913fafec07
  Building wheel for colorclass (setup.py): started
  Building wheel for colorclass (setup.py): finished with status 'done'
  Created wheel for colorclass: filename=colorclass-2.2.0-py3-none-any.whl size=19395 sha256=5bb03eaee7ee682a8db70b8a9cc1e1dc2972a42ccf313d63e5e9a89a3af111f9
  Stored in directory: /root/.cache/pip/wheels/94/c4/e5/8f9dbdb37ddd97e0896de7de36b4d7598df223012918049801
  Building wheel for rebulk (setup.py): started
  Building wheel for rebulk (setup.py): finished with status 'done'
  Created wheel for rebulk: filename=rebulk-2.0.0-py3-none-any.whl size=55506 sha256=892d1c19edc93b68060a569911d6b3ea6f8358cfec1be85621753aea1c1cb3c2
  Stored in directory: /root/.cache/pip/wheels/0d/e4/8c/9a795ed8e5591e2930929b19db5d2e6d4ecc2c03000dff3c56
  Building wheel for terminaltables (setup.py): started
  Building wheel for terminaltables (setup.py): finished with status 'done'
  Created wheel for terminaltables: filename=terminaltables-3.1.0-py3-none-any.whl size=15354 sha256=71546e3f3721b3913d9d9ace294502c758936787b13ed0322093b3e16f133ebf
  Stored in directory: /root/.cache/pip/wheels/86/1b/58/c23af2fe683acd8edc15d5a1268f0242be1ff2cf827fe34737
  Building wheel for feedparser (setup.py): started
  Building wheel for feedparser (setup.py): finished with status 'done'
  Created wheel for feedparser: filename=feedparser-5.2.1-py3-none-any.whl size=44939 sha256=ce27ad61737fca7be84380e5cbbabce18ad48f2056dab123eeb88f12134bbebe
  Stored in directory: /root/.cache/pip/wheels/2f/70/50/16138238f6447854a1300f7d457766789dc7122cfaf46bcef2
  Building wheel for flask-compress (setup.py): started
  Building wheel for flask-compress (setup.py): finished with status 'done'
  Created wheel for flask-compress: filename=Flask_Compress-1.4.0-py3-none-any.whl size=3711 sha256=dec9e0b1cc282c0e9f7d7d3306b0fcbc341f5f481c85ba68ca86bd438c2552cc
  Stored in directory: /root/.cache/pip/wheels/2c/d9/d8/a8a9a3af0e19c7240f1298df7686daa37dc9ea419018ed77d7
  Building wheel for rpyc (setup.py): started
  Building wheel for rpyc (setup.py): finished with status 'done'
  Created wheel for rpyc: filename=rpyc-4.0.1-py3-none-any.whl size=64319 sha256=da4c1ab148f31be66eb99e7c17a84a63fc480ca3b968c4c7e09e5c17346934af
  Stored in directory: /root/.cache/pip/wheels/79/d9/cb/bf12c1364411d5c578f1addb38d9da98338dde3b32cfb19dd3
  Building wheel for pillow (setup.py): started
  Building wheel for pillow (setup.py): finished with status 'error'
  ERROR: Command errored out with exit status 1:
   command: /usr/local/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-rn8zcc9n/pillow/setup.py'"'"'; __file__='"'"'/tmp/pip-install-rn8zcc9n/pillow/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /tmp/pip-wheel-k8gyc9bn
       cwd: /tmp/pip-install-rn8zcc9n/pillow/
  Complete output (172 lines):
  running bdist_wheel
  running build
  running build_py
  creating build
  creating build/lib.linux-x86_64-3.6
  creating build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageChops.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/FitsStubImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/MpoImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageWin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageStat.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageDraw2.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/TarIO.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/FliImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageShow.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PsdImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/FtexImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageEnhance.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/SunImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/JpegPresets.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/BlpImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImagePalette.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/CurImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PcdImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/__init__.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/features.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ContainerIO.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PyAccess.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/JpegImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PaletteFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/GimpGradientFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/GdImageFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/BufrStubImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/DdsImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/XVThumbImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/WmfImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/MpegImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/MicImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/MspImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/TiffTags.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/_binary.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PalmImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageFont.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageQt.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageMath.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PngImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageDraw.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PdfParser.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/IptcImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/Hdf5StubImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageColor.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/_util.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/Jpeg2KImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageGrab.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ExifTags.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/FpxImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/BmpImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/TgaImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImtImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/_tkinter_finder.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/GifImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/IcnsImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PSDraw.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageFilter.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImagePath.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/XpmImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/WebPImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageMorph.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageCms.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/McIdasImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/BdfFontFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/GbrImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/SpiderImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageTk.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PcxImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/TiffImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/__main__.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/XbmImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageTransform.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/_version.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageMode.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/WalImageFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageOps.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PcfFontFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/GimpPaletteFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/ImageSequence.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/FontFile.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/SgiImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/Image.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/DcxImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/GribStubImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PixarImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/IcoImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PdfImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/PpmImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  copying src/PIL/EpsImagePlugin.py -> build/lib.linux-x86_64-3.6/PIL
  running egg_info
  writing src/Pillow.egg-info/PKG-INFO
  writing dependency_links to src/Pillow.egg-info/dependency_links.txt
  writing top-level names to src/Pillow.egg-info/top_level.txt
  reading manifest file 'src/Pillow.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  warning: no files found matching '*.c'
  warning: no files found matching '*.h'
  warning: no files found matching '*.sh'
  warning: no previously-included files found matching '.appveyor.yml'
  warning: no previously-included files found matching '.coveragerc'
  warning: no previously-included files found matching '.codecov.yml'
  warning: no previously-included files found matching '.editorconfig'
  warning: no previously-included files found matching '.readthedocs.yml'
  warning: no previously-included files found matching 'azure-pipelines.yml'
  warning: no previously-included files matching '.git*' found anywhere in distribution
  warning: no previously-included files matching '*.pyc' found anywhere in distribution
  warning: no previously-included files matching '*.so' found anywhere in distribution
  no previously-included directories found matching '.azure-pipelines'
  no previously-included directories found matching '.travis'
  writing manifest file 'src/Pillow.egg-info/SOURCES.txt'
  running build_ext
  
  
  The headers or library files could not be found for zlib,
  a required dependency when compiling Pillow from source.
  
  Please see the install instructions at:
     https://pillow.readthedocs.io/en/latest/installation.html
  
  Traceback (most recent call last):
    File "/tmp/pip-install-rn8zcc9n/pillow/setup.py", line 892, in <module>
      zip_safe=not (debug_build() or PLATFORM_MINGW),
    File "/usr/local/lib/python3.6/site-packages/setuptools/__init__.py", line 144, in setup
      return distutils.core.setup(**attrs)
    File "/usr/local/lib/python3.6/distutils/core.py", line 148, in setup
      dist.run_commands()
    File "/usr/local/lib/python3.6/distutils/dist.py", line 955, in run_commands
      self.run_command(cmd)
    File "/usr/local/lib/python3.6/distutils/dist.py", line 974, in run_command
      cmd_obj.run()
    File "/usr/local/lib/python3.6/site-packages/wheel/bdist_wheel.py", line 223, in run
      self.run_command('build')
    File "/usr/local/lib/python3.6/distutils/cmd.py", line 313, in run_command
      self.distribution.run_command(command)
    File "/usr/local/lib/python3.6/distutils/dist.py", line 974, in run_command
      cmd_obj.run()
    File "/usr/local/lib/python3.6/distutils/command/build.py", line 135, in run
      self.run_command(cmd_name)
    File "/usr/local/lib/python3.6/distutils/cmd.py", line 313, in run_command
      self.distribution.run_command(command)
    File "/usr/local/lib/python3.6/distutils/dist.py", line 974, in run_command
      cmd_obj.run()
    File "/usr/local/lib/python3.6/distutils/command/build_ext.py", line 339, in run
      self.build_extensions()
    File "/tmp/pip-install-rn8zcc9n/pillow/setup.py", line 687, in build_extensions
      raise RequiredDependencyException(f)
  __main__.RequiredDependencyException: zlib
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "<string>", line 1, in <module>
    File "/tmp/pip-install-rn8zcc9n/pillow/setup.py", line 907, in <module>
      raise RequiredDependencyException(msg)
  __main__.RequiredDependencyException:
  
  The headers or library files could not be found for zlib,
  a required dependency when compiling Pillow from source.
  
  Please see the install instructions at:
     https://pillow.readthedocs.io/en/latest/installation.html
  
  
  ----------------------------------------
  ERROR: Failed building wheel for pillow
  Running setup.py clean for pillow
  Building wheel for pynzb (setup.py): started
  Building wheel for pynzb (setup.py): finished with status 'done'
  Created wheel for pynzb: filename=pynzb-0.1.0-py3-none-any.whl size=6233 sha256=9a4acccf15358dc0a8f1e5664d95b3c28c6fec0760fa8b951117fecb69fba212
  Stored in directory: /root/.cache/pip/wheels/4c/e8/1f/6f81b4ca0abff9a2de7a94ce4e1350b857783333225c46705a
  Building wheel for guessit (setup.py): started
  Building wheel for guessit (setup.py): finished with status 'done'
  Created wheel for guessit: filename=guessit-3.1.0-py3-none-any.whl size=162271 sha256=6609300d80e0b5c158180f3f38658f2ac1d7eaac7a8e53d9e7ef83cc47651214
  Stored in directory: /root/.cache/pip/wheels/98/72/68/15226f52eb17873d34111974b83b45768f4911b6a0436d1c6f
  Building wheel for babelfish (setup.py): started
  Building wheel for babelfish (setup.py): finished with status 'done'
  Created wheel for babelfish: filename=babelfish-0.5.5-py3-none-any.whl size=97714 sha256=b53cffd24e1f68c225b0b9b33d8abe0803b2d89d358759e45028942e7b6e688d
  Stored in directory: /root/.cache/pip/wheels/f6/69/2f/9d377135a4c2a8faaebdc9f1ce3a17d9b9171e01100f93ec9d
  Building wheel for pyyaml (setup.py): started
  Building wheel for pyyaml (setup.py): finished with status 'done'
  Created wheel for pyyaml: filename=PyYAML-5.1.2-cp36-cp36m-linux_x86_64.whl size=44104 sha256=c98214d3d373eb1b19d067b9eeb76e4c30d3ab072ed53d19d67386fcbc9f0cc9
  Stored in directory: /root/.cache/pip/wheels/d8/9b/e7/75af463b873c119dd444151fc54a8e190c87993593e1fa194a
  Building wheel for pyrss2gen (setup.py): started
  Building wheel for pyrss2gen (setup.py): finished with status 'done'
  Created wheel for pyrss2gen: filename=PyRSS2Gen-1.1-py3-none-any.whl size=4988 sha256=5c48d8213167bf014755a2169b86b5a38debcbc80e7c3c6ccac76260431fa0cb
  Stored in directory: /root/.cache/pip/wheels/28/1e/f7/e1e6ecd239143aff5d2b2cb6d57301a8ce7c4f7ae3e672cda2
  Building wheel for tzlocal (setup.py): started
  Building wheel for tzlocal (setup.py): finished with status 'done'
  Created wheel for tzlocal: filename=tzlocal-1.4-py3-none-any.whl size=16942 sha256=c3870ade88de0dbe838742fd704aae0b5b8775b01235e081d445c16ab81c0472
  Stored in directory: /root/.cache/pip/wheels/31/06/1b/7e9618d5b0cce0a9d39f244d4c1dbfc36eca6b7dc48edcb859
  Building wheel for contextvars (setup.py): started
  Building wheel for contextvars (setup.py): finished with status 'done'
  Created wheel for contextvars: filename=contextvars-2.4-py3-none-any.whl size=7664 sha256=b41fd7ea78ca70844020f5a23560fe100d46845422ac844ba9ecb6baf54ebc23
  Stored in directory: /root/.cache/pip/wheels/41/11/53/911724983aa48deb94792432e14e518447212dd6c5477d49d3
  Building wheel for immutables (setup.py): started
  Building wheel for immutables (setup.py): finished with status 'error'
  ERROR: Command errored out with exit status 1:
   command: /usr/local/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-rn8zcc9n/immutables/setup.py'"'"'; __file__='"'"'/tmp/pip-install-rn8zcc9n/immutables/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /tmp/pip-wheel-zi00ovgj
       cwd: /tmp/pip-install-rn8zcc9n/immutables/
  Complete output (26 lines):
  running bdist_wheel
  running build
  running build_py
  creating build
  creating build/lib.linux-x86_64-3.6
  creating build/lib.linux-x86_64-3.6/immutables
  copying immutables/__init__.py -> build/lib.linux-x86_64-3.6/immutables
  copying immutables/map.py -> build/lib.linux-x86_64-3.6/immutables
  running egg_info
  writing immutables.egg-info/PKG-INFO
  writing dependency_links to immutables.egg-info/dependency_links.txt
  writing top-level names to immutables.egg-info/top_level.txt
  reading manifest file 'immutables.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  writing manifest file 'immutables.egg-info/SOURCES.txt'
  copying immutables/_map.c -> build/lib.linux-x86_64-3.6/immutables
  copying immutables/_map.h -> build/lib.linux-x86_64-3.6/immutables
  copying immutables/_map.pyi -> build/lib.linux-x86_64-3.6/immutables
  copying immutables/py.typed -> build/lib.linux-x86_64-3.6/immutables
  running build_ext
  building 'immutables._map' extension
  creating build/temp.linux-x86_64-3.6
  creating build/temp.linux-x86_64-3.6/immutables
  gcc -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -DTHREAD_STACK_SIZE=0x100000 -fPIC -I/usr/local/include/python3.6m -c immutables/_map.c -o build/temp.linux-x86_64-3.6/immutables/_map.o -O2 -std=c99 -fsigned-char -Wall -Wsign-compare -Wconversion
  unable to execute 'gcc': No such file or directory
  error: command 'gcc' failed with exit status 1
  ----------------------------------------
  ERROR: Failed building wheel for immutables
  Running setup.py clean for immutables
Successfully built markupsafe itsdangerous aniso8601 zxcvbn-python progressbar sqlalchemy colorclass rebulk terminaltables feedparser flask-compress rpyc pynzb guessit babelfish pyyaml pyrss2gen tzlocal contextvars
Failed to build pillow immutables
Installing collected packages: markupsafe, more-itertools, zc.lockfile, itsdangerous, six, jaraco.functools, cheroot, immutables, contextvars, aiocontextvars, loguru, pytz, jinja2, python-dateutil, aniso8601, werkzeug, zxcvbn-python, click, flask, jsonschema, flask-restplus, plumbum, progressbar, flask-login, idna, sqlalchemy, colorclass, soupsieve, flask-cors, rebulk, flask-restful, terminaltables, feedparser, pyparsing, webencodings, html5lib, certifi, urllib3, chardet, requests, tempora, portend, cherrypy, flask-compress, rpyc, pillow, pynzb, babelfish, guessit, beautifulsoup4, tzlocal, apscheduler, pyyaml, pyrss2gen, python-xlib, pystray, flexget
    Running setup.py install for immutables: started
    Running setup.py install for immutables: finished with status 'error'
    ERROR: Command errored out with exit status 1:
     command: /usr/local/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-rn8zcc9n/immutables/setup.py'"'"'; __file__='"'"'/tmp/pip-install-rn8zcc9n/immutables/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-pa7idnsw/install-record.txt --single-version-externally-managed --compile --install-headers /usr/local/include/python3.6m/immutables
         cwd: /tmp/pip-install-rn8zcc9n/immutables/
    Complete output (26 lines):
    running install
    running build
    running build_py
    creating build
    creating build/lib.linux-x86_64-3.6
    creating build/lib.linux-x86_64-3.6/immutables
    copying immutables/__init__.py -> build/lib.linux-x86_64-3.6/immutables
    copying immutables/map.py -> build/lib.linux-x86_64-3.6/immutables
    running egg_info
    writing immutables.egg-info/PKG-INFO
    writing dependency_links to immutables.egg-info/dependency_links.txt
    writing top-level names to immutables.egg-info/top_level.txt
    reading manifest file 'immutables.egg-info/SOURCES.txt'
    reading manifest template 'MANIFEST.in'
    writing manifest file 'immutables.egg-info/SOURCES.txt'
    copying immutables/_map.c -> build/lib.linux-x86_64-3.6/immutables
    copying immutables/_map.h -> build/lib.linux-x86_64-3.6/immutables
    copying immutables/_map.pyi -> build/lib.linux-x86_64-3.6/immutables
    copying immutables/py.typed -> build/lib.linux-x86_64-3.6/immutables
    running build_ext
    building 'immutables._map' extension
    creating build/temp.linux-x86_64-3.6
    creating build/temp.linux-x86_64-3.6/immutables
    gcc -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -DTHREAD_STACK_SIZE=0x100000 -fPIC -I/usr/local/include/python3.6m -c immutables/_map.c -o build/temp.linux-x86_64-3.6/immutables/_map.o -O2 -std=c99 -fsigned-char -Wall -Wsign-compare -Wconversion
    unable to execute 'gcc': No such file or directory
    error: command 'gcc' failed with exit status 1
    ----------------------------------------
ERROR: Command errored out with exit status 1: /usr/local/bin/python -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-rn8zcc9n/immutables/setup.py'"'"'; __file__='"'"'/tmp/pip-install-rn8zcc9n/immutables/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-pa7idnsw/install-record.txt --single-version-externally-managed --compile --install-headers /usr/local/include/python3.6m/immutables Check the logs for full command output.
The command '/bin/sh -c pip3 install -U pip && pip3 install flexget' returned a non-zero code: 1

Hey mate,

Had the same problem. This is because the docker image they use does not have build tools necessary for building flexget dependencies.

Update your dockerfile like this to add the build binaries first:

FROM     python:alpine

ARG      DOCKER_UID

# Create a user to run the application
RUN      adduser -D -u ${DOCKER_UID} flexget
WORKDIR  /home/flexget

# Data and config volumes
VOLUME   /home/flexget/.flexget
VOLUME   /home/flexget/torrents

# Install FlexGet
RUN      apk add --no-cache --virtual .build-deps gcc musl-dev \
     && pip3 install -U pip && pip3 install flexget \
     && apk del .build-deps gcc musl-dev

# Add start script
COPY     start.sh /home/flexget/
RUN      chmod +x ./start.sh

USER     flexget
CMD      ["./start.sh"]

I updated the wiki page to include build dependencies in the Dockerfile now