Errors when trying to call pycurl in a lambda on AWS - amazon-web-services

Question

I want to use pycurl in order to have TTFB and TTLB, but am unable to call pycurl in an AWS lambda.
To focus on the issue, let say I call this simple lambda function:
import json
import pycurl
import certifi
def lambda_handler(event, context):
client_curl = pycurl.Curl()
client_curl.setopt(pycurl.CAINFO, certifi.where())
client_curl.setopt(pycurl.URL, "https://www.arolla.fr/blog/author/edouard-gomez-vaez/") #set url
client_curl.setopt(pycurl.FOLLOWLOCATION, 1)
client_curl.setopt(pycurl.WRITEFUNCTION, lambda x: None)
content = client_curl.perform()
dns_time = client_curl.getinfo(pycurl.NAMELOOKUP_TIME) #DNS time
conn_time = client_curl.getinfo(pycurl.CONNECT_TIME) #TCP/IP 3-way handshaking time
starttransfer_time = client_curl.getinfo(pycurl.STARTTRANSFER_TIME) #time-to-first-byte time
total_time = client_curl.getinfo(pycurl.TOTAL_TIME) #last requst time
client_curl.close()
data = json.dumps({'dns_time':dns_time,
'conn_time':conn_time,
'starttransfer_time':starttransfer_time,
'total_time':total_time,
})
return {
'statusCode': 200,
'body': data
}
I have the following error, which is understandable:
Unable to import module 'lambda_function': No module named 'pycurl'
I followed the tuto https://aws.amazon.com/fr/premiumsupport/knowledge-center/lambda-layer-simulated-docker/ in order to create a layer, but then have the following error while generated the layer with docker (I extracted the interesting part):
Could not run curl-config: [Errno 2] No such file or directory: 'curl-config': 'curl-config'
I even tried to generate the layer just launching on my own machine:
pip install -r requirements.txt -t python/lib/python3.6/site-packages/
zip -r mypythonlibs.zip python > /dev/null
And then uploading the zip as a layer in aws, but I then have another error when lanching the lambda:
Unable to import module 'lambda_function': libssl.so.1.0.0: cannot open shared object file: No such file or directory
It seems that the layer has to be built on a somehow extended target environment.

Answer 1

After a couple of hours scratching my head, I managed to resolve this issue.
TL;DR: build the layer by using a docker image inherited from the aws one, but with the needed libraries, for instance libcurl-devel, openssl-devel, python36-devel. Have a look at the trick Note 3 :).
The detailed way:
Prerequisite: having Docker installed
In a empty directory, copy your requirements.txt containing pycurl (in my case: pycurl~=7.43.0.5)
In this same directory, create the following Dockerfile (cf Note 3):
FROM public.ecr.aws/sam/build-python3.6
RUN yum install libcurl-devel python36-devel -y
RUN yum install openssl-devel -y
ENV PYCURL_SSL_LIBRARY=openssl
RUN ln -s /usr/include /var/lang/include
Build the docker image:
docker build -t build-python3.6-pycurl .
build the layer using this image (cf Note 2), by running:
docker run -v "$PWD":/var/task "build-python3.6-pycurl" /bin/sh -c "pip install -r requirements.txt -t python/lib/python3.6/site-packages/; exit"
Zip the layer by running:
zip mylayer.zip python > /dev/null
Send the file mylayer.zip to aws as a layer and make your lambda points to it (using the console, or following the tuto https://aws.amazon.com/fr/premiumsupport/knowledge-center/lambda-layer-simulated-docker/).
Test your lambda and celebrate!
Note 1. If you want to use python 3.8, just change 3.6 or 36 by 3.8 and 38.
Note 2. Do not forget to remove the python folder when regenerating the layer, using admin rights if necessary.
Note 3. Mind the symlink in the last line of the DockerFile. Without it, gcc won't be able to find some header files, such as Python.h.
Note 4. Compile pycurl with openssl backend, for it is the ssl backend used in the lambda executing environment. Or else you'll get a libcurl link-time ssl backend (openssl) is different from compile-time ssl backend error when executing the lambda.