Installing EventMachine Gem on OSX El Capitan

If you are running into errors like below when installing EventMachine on OSX El Capitan, its probably because of OpenSsl

Building native extensions.  This could take a while...
ERROR:  Error installing eventmachine:
        ERROR: Failed to build gem native extension.

    current directory: /Users/ismail.kalimi/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/eventmachine-1.0.8/ext
/Users/ismail.kalimi/.rbenv/versions/2.3.1/bin/ruby -r ./siteconf20170619-62544-n32z9e.rb extconf.rb
checking for rb_trap_immediate in ruby.h,rubysig.h... no
checking for rb_thread_blocking_region()... no
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for inotify_init() in sys/inotify.h... no
checking for __NR_inotify_init in sys/syscall.h... no
checking for writev() in sys/uio.h... yes
checking for rb_thread_fd_select()... yes
checking for rb_fdset_t in ruby/intern.h... yes
checking for pipe2() in unistd.h... no
checking for accept4() in sys/socket.h... no
checking for SOCK_CLOEXEC in sys/socket.h... no
checking for rb_wait_for_single_fd()... yes
checking for rb_enable_interrupt()... no
checking for rb_time_new()... yes
checking for sys/event.h... yes
checking for sys/queue.h... yes
CFLAGS= -O3 -Wno-error=shorten-64-to-32  -pipe  -Wall -Wextra -Wno-deprecated-declarations -Wno-ignored-qualifiers -Wno-unused-result
CPPFLAGS=-I/Users/ismail.kalimi/.rbenv/versions/2.3.1/include  -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT $(DEFS) $(cppflags) -Wall -Wextra -Wno-deprecated-declarations -Wno-ignored-qualifiers -Wno-unused-result
checking for clock_gettime()... no
checking for gethrtime()... no
creating Makefile

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/ismail.kalimi/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/eventmachine-1.0.8/mkmf.log

current directory: /Users/ismail.kalimi/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/eventmachine-1.0.8/ext
make "DESTDIR=" clean

current directory: /Users/ismail.kalimi/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/eventmachine-1.0.8/ext
make "DESTDIR="
compiling binder.cpp
In file included from binder.cpp:20:
./project.h:116:10: fatal error: 'openssl/ssl.h' file not found
#include <openssl/ssl.h>
         ^
1 error generated.
make: *** [binder.o] Error 1

make failed, exit code 2

Gem files will remain installed in /Users/ismail.kalimi/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/eventmachine-1.0.8 for inspection.
Results logged to /Users/ismail.kalimi/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/eventmachine-1.0.8/gem_make.out

Make sure openssl is installed through brew

brew install openssl

Then pass the following flag with the install

gem install eventmachine -- --with-cppflags="-I/usr/local/opt/openssl/include"

Credit: nownabe