llnw-cdn

Technical interview task put forward by Limelight Networks to build, implement and demonstrate a small content delivery network.

Technology

• Terraform
• Ansible
• AWS Lightsail
• Ubuntu
• Nginx
• Varnish

Step 1 - init terraform

In the top level directory of this project, on command line run:
terraform init

Step 2 - provision infrastructure

Use terraform to deploy edges and origins run:
terraform apply

Step 3 - configure the application

Use ansible to configure the newly provisioned infrastructure.
ansible-playbook -i inventory.cfg -u ubuntu setup.yml

Debug header

curl -svo /dev/null http://edge.llnw.mcnulty.network/ -H "x-secret-debug-header: yes"

Noteworthy points

I manually created the hosted zone in AWS as it means that I won't have to update my name servers on every terraform redeploy. Fallback index.html on nginx lives at sudo vim /usr/share/nginx/html/index.html terraform show | egrep "^#" list terraform by name Cache keys will involve the hostname i.e. localhost is not the same as edge-1.llnw.mcnulty.network so need to cater for both when purging

Running this within PSSH allows me to purge the local cache version on the box but also the client facing or header curl -svo /dev/null --resolve edge.llnw.mcnulty.network:80:127.0.0.1 http://edge.llnw.mcnulty.network/myfile -X PURGE -H "x-secret-purge-header: yes"

Useful Resources Found

https://varnish-cache.org/docs/trunk/users-guide/vcl-hashing.html
https://linux.die.net/man/1/pssh

Stretch Ideas

• Create ansible playbooks for the local client machine orchestrating these changes to make adoption easier.
• Provide a means of carrying out purge across all edges (pssh or orchestrated edge to edge communication).
• Use pssh to pull all the varnishlog to demo how many requests
• Provide a certificate using LetsEncrypt for each node, either locally and pushing it or allowing the nodes to manage their own for TLS termination.