You repository seams to have a problem:

http://repo.zabbix.com/zabbix/4.2/rhel/7/x86_64/zabbix-web-4.2.6-1.el7.noarch.rpm

The following step 

yum -y install zabbix-server-mysql zabbix-web-mysql zabbix-agent

fails with this error : 

zabbix-web-4.2.6-1.el7.noarch. FAILED 0% [ ] 0.0 B/s | 0 B -::- ETA
http://repo.zabbix.com/zabbix/4.2/rhel/7/x86_64/zabbix-web-4.2.6-1.el7.noarch.rpm: [Errno 14] curl#18 - "transfer closed with 2907273 bytes remaining to read" B/s | 0 B -::- ETA
Trying other mirror.

Error downloading packages:
zabbix-web-4.2.6-1.el7.noarch: [Errno 256] No more mirrors to try.