Build is working for me, also on a fresh checkout. The error you get before git fails (ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.12/main: temporary error (try again later))makes it so that you can't install git.

You might want to try again. Are you connected to an enterprise network ? The connection is established via HTTP, which might be blocked on some network or the domain itself (dl-cdn.alpinelinux.org) is blocked. Try to connect and if it fails ask your network administrator to allow the connection.

If you can't/it's against internal policies, you'll need to create an internal repository that provides the needed dependencies. Or You may want to edit the list of repositories the container talks to to use an internal/allowed repository instead of the default. This will require that you edit the dockerfile or create a custom image for the build.

# docker build -t photon .
Sending build context to Docker daemon    555kB
Step 1/12 : FROM python:3-alpine
3-alpine: Pulling from library/python
df20fa9351a1: Pulling fs layer
36b3adc4ff6f: Pulling fs layer
7031d6d6c7f1: Pulling fs layer
81b7f5a7444b: Pulling fs layer
0f8a54c5d7c7: Pulling fs layer
81b7f5a7444b: Waiting
0f8a54c5d7c7: Waiting
df20fa9351a1: Verifying Checksum
81b7f5a7444b: Verifying Checksum
81b7f5a7444b: Download complete
0f8a54c5d7c7: Verifying Checksum
0f8a54c5d7c7: Download complete
df20fa9351a1: Pull complete
36b3adc4ff6f: Verifying Checksum
36b3adc4ff6f: Download complete
7031d6d6c7f1: Verifying Checksum
7031d6d6c7f1: Download complete
36b3adc4ff6f: Pull complete
7031d6d6c7f1: Pull complete
81b7f5a7444b: Pull complete
0f8a54c5d7c7: Pull complete
Digest: sha256:c5623df482648cacece4f9652a0ae04b51576c93773ccd43ad459e2a195906dd
Status: Downloaded newer image for python:3-alpine
 ---> 8ecf5a48c789
Step 2/12 : LABEL name photon
 ---> Running in fa51c0ea836b
Removing intermediate container fa51c0ea836b
 ---> 1ac81175343b
Step 3/12 : LABEL src "https://github.com/s0md3v/Photon"
 ---> Running in 425691ce0844
Removing intermediate container 425691ce0844
 ---> 2371c58b7bd5
Step 4/12 : LABEL creator s0md3v
 ---> Running in 3d50cab500a7
Removing intermediate container 3d50cab500a7
 ---> 04520e48361c
Step 5/12 : LABEL dockerfile_maintenance khast3x
 ---> Running in 0dac63839b50
Removing intermediate container 0dac63839b50
 ---> 95a06d6ab65a
Step 6/12 : LABEL desc "Incredibly fast crawler designed for reconnaissance."
 ---> Running in f08f9e0c09f5
Removing intermediate container f08f9e0c09f5
 ---> 9beb0b499ca9
Step 7/12 : RUN apk add git && git clone https://github.com/s0md3v/Photon.git Photon
 ---> Running in f43e11785817
fetch http://dl-cdn.alpinelinux.org/alpine/v3.12/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.12/community/x86_64/APKINDEX.tar.gz
(1/4) Installing nghttp2-libs (1.41.0-r0)
(2/4) Installing libcurl (7.69.1-r0)
(3/4) Installing pcre2 (10.35-r0)
(4/4) Installing git (2.26.2-r0)
Executing busybox-1.31.1-r16.trigger
OK: 27 MiB in 39 packages
Cloning into 'Photon'...
Removing intermediate container f43e11785817
 ---> e7b0de06e0a4
Step 8/12 : WORKDIR Photon
 ---> Running in 7107359d12d0
Removing intermediate container 7107359d12d0
 ---> d69e981c9ec7
Step 9/12 : RUN pip install -r requirements.txt
 ---> Running in 3c70b11a95ff
Collecting requests
  Downloading requests-2.23.0-py2.py3-none-any.whl (58 kB)
Collecting urllib3
  Downloading urllib3-1.25.9-py2.py3-none-any.whl (126 kB)
Collecting tld
  Downloading tld-0.12.2-py38-none-any.whl (329 kB)
Collecting certifi>=2017.4.17
  Downloading certifi-2020.4.5.2-py2.py3-none-any.whl (157 kB)
Collecting idna<3,>=2.5
  Downloading idna-2.9-py2.py3-none-any.whl (58 kB)
Collecting chardet<4,>=3.0.2
  Downloading chardet-3.0.4-py2.py3-none-any.whl (133 kB)
Installing collected packages: certifi, idna, urllib3, chardet, requests, tld
Successfully installed certifi-2020.4.5.2 chardet-3.0.4 idna-2.9 requests-2.23.0 tld-0.12.2 urllib3-1.25.9
Removing intermediate container 3c70b11a95ff
 ---> 8ec4974e7e03
Step 10/12 : VOLUME [ "/Photon" ]
 ---> Running in 560e249202d2
Removing intermediate container 560e249202d2
 ---> d8d8e807a175
Step 11/12 : ENTRYPOINT [ "python", "photon.py" ]
 ---> Running in 442ed5a3ff46
Removing intermediate container 442ed5a3ff46
 ---> 58bd5796d8d6
Step 12/12 : CMD ["--help"]
 ---> Running in f3b986bfe744
Removing intermediate container f3b986bfe744
 ---> 03a338712d83
Successfully built 03a338712d83
Successfully tagged photon:latest

from photon.

Check the update:

docker build -t photon .

Sending build context to Docker daemon 555kB
Step 1/12 : FROM python:3-alpine
3-alpine: Pulling from library/python
df20fa9351a1: Pulling fs layer
36b3adc4ff6f: Pulling fs layer
7031d6d6c7f1: Pulling fs layer
81b7f5a7444b: Pulling fs layer
0f8a54c5d7c7: Pulling fs layer
81b7f5a7444b: Waiting
0f8a54c5d7c7: Waiting
df20fa9351a1: Verifying Checksum
81b7f5a7444b: Verifying Checksum
81b7f5a7444b: Download complete
0f8a54c5d7c7: Verifying Checksum
0f8a54c5d7c7: Download complete
df20fa9351a1: Pull complete
36b3adc4ff6f: Verifying Checksum
36b3adc4ff6f: Download complete
7031d6d6c7f1: Verifying Checksum
7031d6d6c7f1: Download complete
36b3adc4ff6f: Pull complete
7031d6d6c7f1: Pull complete
81b7f5a7444b: Pull complete
0f8a54c5d7c7: Pull complete
Digest: sha256:c5623df482648cacece4f9652a0ae04b51576c93773ccd43ad459e2a195906dd
Status: Downloaded newer image for python:3-alpine
---> 8ecf5a48c789
Step 2/12 : LABEL name photon
---> Running in fa51c0ea836b
Removing intermediate container fa51c0ea836b
---> 1ac81175343b
Step 3/12 : LABEL src "https://github.com/s0md3v/Photon"
---> Running in 425691ce0844
Removing intermediate container 425691ce0844
---> 2371c58b7bd5
Step 4/12 : LABEL creator s0md3v
---> Running in 3d50cab500a7
Removing intermediate container 3d50cab500a7
---> 04520e48361c
Step 5/12 : LABEL dockerfile_maintenance khast3x
---> Running in 0dac63839b50
Removing intermediate container 0dac63839b50
---> 95a06d6ab65a
Step 6/12 : LABEL desc "Incredibly fast crawler designed for reconnaissance."
---> Running in f08f9e0c09f5
Removing intermediate container f08f9e0c09f5
---> 9beb0b499ca9
Step 7/12 : RUN apk add git && git clone https://github.com/s0md3v/Photon.git Photon
---> Running in f43e11785817
fetch http://dl-cdn.alpinelinux.org/alpine/v3.12/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.12/community/x86_64/APKINDEX.tar.gz
(1/4) Installing nghttp2-libs (1.41.0-r0)
(2/4) Installing libcurl (7.69.1-r0)
(3/4) Installing pcre2 (10.35-r0)
(4/4) Installing git (2.26.2-r0)
Executing busybox-1.31.1-r16.trigger
OK: 27 MiB in 39 packages
Cloning into 'Photon'...
Removing intermediate container f43e11785817
---> e7b0de06e0a4
Step 8/12 : WORKDIR Photon
---> Running in 7107359d12d0
Removing intermediate container 7107359d12d0
---> d69e981c9ec7
Step 9/12 : RUN pip install -r requirements.txt
---> Running in 3c70b11a95ff
Collecting requests
Downloading requests-2.23.0-py2.py3-none-any.whl (58 kB)
Collecting urllib3
Downloading urllib3-1.25.9-py2.py3-none-any.whl (126 kB)
Collecting tld
Downloading tld-0.12.2-py38-none-any.whl (329 kB)
Collecting certifi>=2017.4.17
Downloading certifi-2020.4.5.2-py2.py3-none-any.whl (157 kB)
Collecting idna<3,>=2.5
Downloading idna-2.9-py2.py3-none-any.whl (58 kB)
Collecting chardet<4,>=3.0.2
Downloading chardet-3.0.4-py2.py3-none-any.whl (133 kB)
Installing collected packages: certifi, idna, urllib3, chardet, requests, tld
Successfully installed certifi-2020.4.5.2 chardet-3.0.4 idna-2.9 requests-2.23.0 tld-0.12.2 urllib3-1.25.9
Removing intermediate container 3c70b11a95ff
---> 8ec4974e7e03
Step 10/12 : VOLUME [ "/Photon" ]
---> Running in 560e249202d2
Removing intermediate container 560e249202d2
---> d8d8e807a175
Step 11/12 : ENTRYPOINT [ "python", "photon.py" ]
---> Running in 442ed5a3ff46
Removing intermediate container 442ed5a3ff46
---> 58bd5796d8d6
Step 12/12 : CMD ["--help"]
---> Running in f3b986bfe744
Removing intermediate container f3b986bfe744
---> 03a338712d83
Successfully built 03a338712d83
Successfully tagged photon:latest

from photon.