Flex missing when building ebpf module on amazon linux2

[schans]

Describe the bug

The build fails on the latest amazon linux.

falco-crdpc falco * Setting up /usr/src links from host
falco-crdpc falco * Running falco-driver-loader with: driver=bpf, compile=yes, download=yes
falco-crdpc falco * Mounting debugfs
falco-crdpc falco * Found kernel config at /host/boot/config-5.4.91-41.139.amzn2.x86_64
falco-crdpc falco * Using downloaded kernel sources for kernel version 5.4.91...
falco-crdpc falco * Downloading http://mirrors.edge.kernel.org/pub/linux/kernel/v5.x/linux-5.4.91.tar.gz
falco-crdpc falco * Extracting kernel sources
falco-crdpc falco * Configuring kernel
falco-crdpc falco /bin/sh: 1: flex: not found
falco-crdpc falco make[1]: *** [scripts/Makefile.host:9: scripts/kconfig/lexer.lex.c] Error 127
falco-crdpc falco make: *** [Makefile:590: olddefconfig] Error 2
falco-crdpc falco /bin/sh: 1: flex: not found
falco-crdpc falco make[2]: *** [scripts/Makefile.host:9: scripts/kconfig/lexer.lex.c] Error 127
falco-crdpc falco make[1]: *** [Makefile:590: syncconfig] Error 2
falco-crdpc falco Makefile:678: include/config/auto.conf.cmd: No such file or directory
falco-crdpc falco make: *** [Makefile:696: include/config/auto.conf.cmd] Error 2

How to reproduce it

Build the ebpf module from source.

Expected behaviour

The module should build successfully

Screenshots

Amazon Linux 2 / EKS 1.19

• Falco version:

Falco version 0.26.2 and 0.27.0

• System info:

5.4.91-41.139.amzn2.x86_64

• Cloud provider or hardware configuration:
• OS:

Amazon Linux2

• Kernel:

5.4.91-41.139.amzn2.x86_64

• Installation method:

Chart with building module from source

Additional context

[schans]

Is there an option to install the flex package with some workaround before the kernel gets build?

[schans]

I just realized: this issue might be better suited in the charts repo perhaps. Let me know if so and I'll move it over.

Or.. we might need to add flex here:

https://github.com/falcosecurity/falco/blob/master/docker/falco/Dockerfile