I don't know why SELinux problems seem so frustrating. The problem almost certainly is related to the fact that there is frequently no error message. This is exactly the problem I ran into while turning up a new Apache web server on Red Hat Enterprise Linux 6 (RHEL6) with SELinux enabled.
The problem is that SELinux prevents Apache from making network connections by default. This is defined by the SELinux boolean
httpd_can_network_connect_db. In order to change this value, issue the following command:
# setsebool -P httpd_can_network_connect_db true
-P indicates the command is persistent and that the setting should survive reboots.
For reference, here is a list of all httpd-related SELinux booleans and their default values in RHEL6:
# getsebool -a | egrep '^httpd' httpd_builtin_scripting --> on httpd_can_check_spam --> off httpd_can_network_connect --> off httpd_can_network_connect_cobbler --> off httpd_can_network_connect_db --> off httpd_can_network_memcache --> off httpd_can_network_relay --> off httpd_can_sendmail --> off httpd_dbus_avahi --> on httpd_enable_cgi --> on httpd_enable_ftp_server --> off httpd_enable_homedirs --> off httpd_execmem --> off httpd_manage_ipa --> off httpd_read_user_content --> off httpd_setrlimit --> off httpd_ssi_exec --> off httpd_tmp_exec --> off httpd_tty_comm --> on httpd_unified --> on httpd_use_cifs --> off httpd_use_gpg --> off httpd_use_nfs --> off httpd_use_openstack --> off