Docker container always shows ssl connection error - python-3.x

Question

I'm getting started with docker compose and have been working through the simple demo flask application. The thing is, I'm running this from inside of an organization that intercepts all communication in such a way that SSL errors are thrown right and left. They provide us with three root certificates we need to install, and I've generally got these working on my own machine, but I'm lost when it comes to getting these to work inside docker-compose deployments.
When I run docker-compose up, I get the following:
$ sudo docker-compose up
Creating network "project_default" with the default driver
Building web
Step 1/5 : FROM python:3.4-alpine
3.4-alpine: Pulling from library/python
81033e7c1d6a: Pull complete
9b61101706a6: Pull complete
415e2a07c89b: Pull complete
f22df7a3f000: Pull complete
8c16bf19c1f9: Pull complete
Digest: sha256:fe436cb066394d81cf49448a04dec7c765082445a500bc44f1ae5e8a455793bd
Status: Downloaded newer image for python:3.4-alpine
---> 5c72717ec319
Step 2/5 : ADD . /code
---> a5790c0e3e94
Removing intermediate container 052c614e41d0
Step 3/5 : WORKDIR /code
---> a2ea9acb3005
Removing intermediate container 77f2375ca0a6
Step 4/5 : RUN pip install -r requirements.txt
---> Running in 5f4fe856776d
Collecting flask (from -r requirements.txt (line 1))
Retrying (Retry(total=4, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb0061f1d30>: Failed to establish a new connection: [Errno -3] Try again',)': /simple/flask/
Retrying (Retry(total=3, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb0061f19b0>: Failed to establish a new connection: [Errno -3] Try again',)': /simple/flask/
Retrying (Retry(total=2, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb0061f1828>: Failed to establish a new connection: [Errno -3] Try again',)': /simple/flask/
Retrying (Retry(total=1, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb0061f1588>: Failed to establish a new connection: [Errno -3] Try again',)': /simple/flask/
Retrying (Retry(total=0, connect=None, read=None, redirect=None)) after connection broken by 'NewConnectionError('<pip._vendor.requests.packages.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb0061f1390>: Failed to establish a new connection: [Errno -3] Try again',)': /simple/flask/
Could not find a version that satisfies the requirement flask (from -r requirements.txt (line 1)) (from versions: )
No matching distribution found for flask (from -r requirements.txt (line 1))
Pip fails to install anything.
The docker-compose.yml file looks like this:
version: '3'
services:
web:
build: .
ports:
- "5000:5000"
redis:
image: "redis:alpine"
And the main Dockerfile looks like this:
FROM python:3.4-alpine
ADD . /code
WORKDIR /code
RUN pip install -r requirements.txt
CMD ["python", "app.py"]
Is there any way to be able to make this work in this particular case? Is there a general solution to this sort of problem that would allow me to pass to any container deployed the SSL certificates and have them be used?

Answer 1

In my case, I must add in my Dockerfile these sentences:
COPY company.crt /usr/local/share/ca-certificates/company.crt
RUN update-ca-certificates
...
RUN pip install --cert /etc/ssl/certs/company.pem -r requirements.txt
You need the certificate of your company in .crt format. When docker execute update-ca-certificates, linux will create a .pem file with the same name in the path: /etc/ssl/certs/. It will convert the network between pip in SSL.

Answer 2

This isn't really a docker-specific question: you are asking, in effect, "how do I install certificate authorities under Linux"? The answer is going to be the same regardless of whether you are running your ssl client inside or outside of a container.
Your Python image is based on alpine, and alpine uses the "ca-certificates" package to manage CA certificiates. To install your local CA certificates, you would need to (a) copy them into the /usr/share/ca-certificates directory and (b) run update-ca-certificates.
For example, adding something like this to your Dockerfile (before your pip install):
COPY company-ca.crt /usr/share/ca-certificates
RUN update-ca-certificates

Answer 3

In my case, Host machine's MTU is 1450, and Docker's MTU is 1500.
Which causes docker set MSS to 1460, and then TLS "server hello" packet got bigger than 1450 bytes, so the Host machine discard it.
To see if it's your case too, run ifconfig on both you Docker container and your host machine. If Host's MTU is less than 1500, it's easy to run into this discarding packet situation. Especially in HTTPS, for that "server hello" needs to send the certificate, which is a big packet

Answer 4

I was trying to read data from an API in my Go code and I was facing similar ssl error:
x509: certificate signed by unknown authority
My container was based on debian:stretch which is really really small ~100MB.
This happens when ca-certificates are not installed.
I installed ca-certificates (which also installs openssl) as shown below:
FROM debian:stretch
RUN apt-get update && apt-get install -y ca-certificates --no-install-recommends && rm -rf /var/lib/apt/lists/*
# ...
This will also work for any other base images which might not have ca-certificates installed.