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Scripts to Stand Up a Demo Kafka Cluster

Introduction

This is a collection of Terraform scripts and Ansible playbooks needed to stand up a zookeeper+kafka cluster on Digital Ocean, suitable for development and demonstration purposes. It is based on the ZADS deployment scripts, with cluster operation and provisioning via Ansible being the key difference.

Description of the deployed cluster

  • The base operating system is CentOS 7.

  • The scripts create a cluster of $NUM_BROKERS (default: 4) kafka brokers, with a zookeeper running at each broker. This can be overridden by editing the settings.auto.tfvars file.

  • All machines in the cluster have a public (eth0) and private (eth1) network interface. Both Zookeeper and Kafka brokers are configured to communicate only on the private interface only (thus avoiding network bandwith charges). We recommend a science platform (e.g., JupyterHub on k8s) be deployed within the same Digital Ocean project, to allow access to the broker through the private interface.

  • All Kafka instances export Prometheus-compatible JMX metrics on port 8080.

  • The DNS names of the machines are brokerN.do.alerts.wtf (private) and ssh-brokerN.do.alerts.wtf (public interface), with N being an ID running from 0 to $NUM_BROKERS-1. As indicated by the name, the public DNS names are largely for ssh access while debugging.

  • The default replication factor is 2, and default number of partitions is 16. Partitions are lz4-compressed by default. Messages are retained for 1 day by default, and offsets for 2 days (1440 minutes). Edit inventory/hosts.yml to customize.

  • The first broker (broker0) comes with one night of ZTF alerts preinstalled, and an ingestion script that you can run to simulate nightly observations. See below for how to use it.

  • WARNING: There is no authentication or authorization. Anyone can create or delete topics. Do not deploy this w/o a firewall or for production.

  • Default firewall configuration blocks everything but ssh on the public interface. The private interface is fully trusted (no firewalling).

Prerequisites

  • You will need Ansible, Terraform, jq, and a Digital Ocean account. Assuming you're using brew as your package manager, run:

    brew install terraform
brew install ansible
brew install jq

    to install the tools.

    You will also need these Ansible roles and plugins:

    ansible-galaxy install andrewrothstein.miniconda

mkdir -p ~/.ansible/plugins/modules
curl -o ~/.ansible/plugins/modules/conda.py https://raw.githubusercontent.com/UDST/ansible-conda/master/conda.py

  • Next, you will need Confluent's Ansible playbooks for Kafka:

    git clone git@github.com:confluentinc/cp-ansible

    (make sure you run this in the current directory; the Makefile expects it there).

    $ cat do_token.auto.tfvars
do_token = "abcdef0123456789abcdef0123456789abcdef0123456789abcdef0123456789"

  • You will need an SSH key (registered with Digital Ocean) which will be authorized to log into the newly created nodes. Specify the MD5 fingerprint of the key in the settings.auto.tfvars file (it's the fingerprint show in DO's Account|Security tab).

  • Finaly, your Digital Ocean account will have to host a DNS domain within which all created brokers will live. The default domain is do.alerts.wtf -- make sure you replace it with your own by adding it to settings.auto.tfvars.

Customization

Basic customization is possible through the settings.auto.tfvars file:

$ cat settings.auto.tfvars
num_brokers = 4
domain = "do.alerts.wtf"
ssh_fingerprint = [ "57:c0:dd:35:2a:06:67:d1:15:ba:6a:74:4d:7c:1c:21" ]

For detailed customization of broker configuration, etc., edit the variables in the Ansible inventory file in inventory/hosts.yml.

Creating a cluster

First, make sure you have all the prerequisites installed (see above). Then run:

# Initialize terraform
terraform init

# Import the information about the domain where the hosts will reside
terraform import digitalocean_domain.default do.alerts.wtf

# Create the VMs (using terraform)
make cluster

# Provision the VMs (using ansible)
make provision

Once the VMs are created and provisioned, a Kafka should be running at brokerN.do.alerts.wtf:9092 (note: these are all private interfaces, inaccessible from the outside).

Testing

One night of ZTF alerts will be uploaded to broker0:/root/alerts, together with an injection script which can inject batches of alerts onto topics to simulate survey-like operation.

For example, to inject 10000 alerts every 40 seconds to a topic named lsst, from the /root/alerts directory on broker0 run:

[root@broker0 alerts]# ../inject.sh lsst 40 10000
Preparing chunks (10000 alerts each)... done (28 chunks).
[Thu Nov 14 16:43:59 PST 2019] injecting tmp-visit.aa to lsst ... done (6 seconds)
[Thu Nov 14 16:44:39 PST 2019] injecting tmp-visit.ab to lsst ... done (6 seconds)

(hit CTRL-C to stop).

You should be able to see that alerts are being injected using (e.g.) kt:

[root@broker0 alerts]# kt topic -partitions -filter 'lsst' | jq -r '.name as $name | .partitions[] | [$name, .id, .oldest, .newest] | @tsv' | sort
lsst	0	0	1040
lsst	10	0	1285
lsst	1	0	1263
lsst	11	0	1169
lsst	12	0	1248
lsst	13	0	1371
lsst	14	0	1326
lsst	15	0	1257
lsst	2	0	1301
lsst	3	0	1158
lsst	4	0	1254
lsst	5	0	1407
lsst	6	0	1349
lsst	7	0	1246
lsst	8	0	1086
lsst	9	0	1240

(where the topic contents have been broken out by partition).

For the total number of alerts in a topic, run:

[root@broker0 alerts]# kt topic -partitions -filter 'lsst' | jq -r '.name as $name | .partitions[] | [$name, .id, .oldest, .newest] | @tsv' | awk '{a[$1]+=$4-$3} END {for(i in a) print i"\t"a[i]}' | sort
lsst	20000

Destroying the cluster

To destroy an existing cluster, run:

make destroy