ELK stack cluster health yellow and Kibana doesn't work

I am trying-out installing and setting up ELK stack on AWS. However I'm having trouble with Logstash and Kibana. I currently have 2 Elastic search instances and they are load balanced and working well. However, when I hit http://load_balance_url:9200/_plugin/head/ , I get the following result:

And when I load Kibana URL, this is what I get:

Kibana: Unknown error while connecting to Elasticsearch Error: Internal Server Error at respond (KIBANA_URL:5601/index.js?_b=5930:81566:15) at checkRespForFailure (KIBANA_URL/index.js?_b=5930:81534:7) at KIBANA_URL:5601/index.js?_b=5930:80203:7 at wrappedErrback (KIBANA_URL:5601/index.js?_b=5930:20882:78) at wrappedErrback (KIBANA_URL:5601/index.js?_b=5930:20882:78) at wrappedErrback (KIBANA_URL:5601/index.js?_b=5930:20882:78) at KIBANA_URL:5601/index.js?_b=5930:21015:76 at Scope.$eval (KIBANA_URL:5601/index.js?_b=5930:22002:28) at Scope.$digest (KIBANA_URL:5601/index.js?_b=5930:21814:31) at Scope.$apply (KIBANA_URL:5601/index.js?_b=5930:22106:24)

I have been following along this tutorial and you can imagine most of settings in my AWS is same as in the video.

http://ift.tt/1BTscDS

Under instances tag of my load balancer, it says I have 2 exact instances with following status Name: Elasticsearch, zone: ap-southeast-1a, Status: InService

And I have 2 available subnets but one states it is "No (Availability Zone contains no healthy instances)"

subnet 1: zone: ap-southeast-1b Subnet CIDR: 172.31.0.0/20 Instance Count: 0 Healthy?: No (Availability Zone contains no healthy instances)

subnet 2

zone: ap-southeast-1a Subnet CIDR: 172.31.16.0/20 Instance Count: 2 Healthy?: Yes

Elasticsearch config:

cluster.name: awstutorialseries

cloud.aws.access_key: my aws access key

cloud.aws.secret_key: my aws secret key

cloud.aws.region: ap-southeast-1a

discovery.type: ec2

discovery.ec2.tag.Name: "AWS Tutorial Series - Elasticsearch"

http.cors.enabled: true

http.cors.allow-origin: "*"

Please help me out with troubleshooting it. Please leave in the reply if you need more information from my current set up. Thank you.