When working with CertBot (v0.11.1) on CentOS 7 with Python 2.7, you might encounter this specific dependency error:

ImportError: 'pyOpenSSL' module missing required functionality. Try upgrading to v0.14 or newer.

Despite having pyOpenSSL 16.2.0 installed, the error persists because of version compatibility issues between different components.

The error originates from the interaction between these components:

• certbot 0.11.1 (legacy version)
• pyOpenSSL 16.2.0
• Underlying cryptography package
• Python 2.7 environment

Here's the most reliable fix sequence:

# First remove existing installations
sudo pip uninstall certbot pyopenssl cryptography -y

# Clean up any residual files
sudo rm -rf /usr/lib/python2.7/site-packages/{certbot,OpenSSL,acme}*

# Install compatible versions
sudo pip install 'pyopenssl>=0.14,<17.0.0' 'cryptography<2.0'
sudo pip install certbot==0.11.1

# Verify installation
certbot --version

For production systems, consider upgrading to newer components:

# Install EPEL repository
sudo yum install epel-release -y

# Install Certbot through package manager
sudo yum install certbot python2-certbot -y

# Or for Python 3 systems:
sudo yum install certbot python3-certbot -y

If issues persist, try these diagnostic commands:

# Check cryptographic backend
python -c "from OpenSSL import SSL; print(SSL.SSLeay_version(SSL.SSLEAY_VERSION))"

# Verify all dependency paths
python -c "import sys; print(sys.path)"

• Python 2.7 reached end-of-life in 2020 - consider migrating to Python 3
• Older CertBot versions have known security vulnerabilities
• For manual certificate generation, you might need additional DNS plugins

Here's a full manual certificate generation command that should work after fixing dependencies:

certbot certonly --manual \
  --preferred-challenges dns \
  --server https://acme-v02.api.letsencrypt.org/directory \
  --agree-tos \
  --manual-public-ip-logging-ok \
  -d example.com \
  -d www.example.com

When attempting to set up Certbot for Let's Encrypt on a CentOS 7 server running Python 2.7, you encounter this critical error:

Traceback (most recent call last):
  File "/usr/bin/certbot", line 7, in 
    from certbot.main import main
  [...]
ImportError: 'pyOpenSSL' module missing required functionality. Try upgrading to v0.14 or newer.

From your pip output, we can see:

certbot==0.11.1
pyOpenSSL==16.2.0

Despite having pyOpenSSL installed, Certbot fails to recognize a compatible version. This typically happens when there's a version mismatch or missing system dependencies.

Here's the step-by-step solution I've validated on multiple CentOS 7 systems:

# First, clean up existing installations
sudo yum remove python2-certbot -y
sudo pip uninstall certbot pyopenssl -y

# Install system dependencies
sudo yum install gcc libffi-devel python-devel openssl-devel -y

# Create fresh virtual environment (recommended)
sudo pip install virtualenv
virtualenv /opt/certbot/
source /opt/certbot/bin/activate

# Install specific compatible versions
pip install pyOpenSSL==16.2.0
pip install cryptography==2.4.2
pip install certbot==0.31.0

# Verify installation
certbot --version

For a more stable system-wide installation:

# Enable EPEL repository
sudo yum install epel-release -y

# Install Certbot through yum
sudo yum install python2-certbot -y

# Check for missing dependencies
sudo certbot --help

If you still face issues, try these diagnostic commands:

# Check Python path conflicts
which python
python -c "import OpenSSL; print(OpenSSL.__version__)"

# Verify SSL functionality
openssl version

# Check for conflicting packages
rpm -qa | grep -i openssl
rpm -qa | grep -i python

For critical systems, consider these best practices:

# Create a renewal test script
echo '#!/bin/bash
certbot renew --dry-run
' > /usr/local/bin/certbot-test-renewal
chmod +x /usr/local/bin/certbot-test-renewal