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Demonstrating a setup of ScyllaDB (in Docker) and a short demo program

Retrieve latest version of ScyllaDB from the Docker registry

docker pull scylladb/scylla

Prepare for setting up ScyllaDB in a local development cluster

We want the Scylla containers to store it's database files outside of the ephemeral container. In order to achieve this, we will provide a local directory (in my case ~/scylla/mapped) to all Scylla containers, which is mounted as a volume in the container (cf. the following figure).

Image

By keeping the database files outside of the Scylla containers, the data will survive the lifetime(s) of the individual Scylla containers.

The last piece of information we need is that each ScyllaDB instance is configured by means of the file /etc/scylla/scylla.yaml within each respective container. We want to provide a uniqe configuration file to each ScyllaDB instance and the easiest way to do this is to externalize this file from each container.

The default ScyllaDB configuration file is present as /etc/scylla/scylla.yaml in the scylladb/scylla image but we will overlay it with our own configuration file -- one unique file per ScyllaDB instance (i.e. one unique file per Scylla container).

Using raw Docker, we will have to be explicit about network ports, but more on that later on.

Prepare configuration

First we need to determine a suitable configuration file template for our setup. We want to do this since we need to modify the configuration of at least one ScyllaDB instance (in order to authenticate for keyspace creation) and possibly for all ScyllaDB instances.

You could start by retrieving a template from GitHub, but it may differ from the one bundled with the Scylla image (which in fact it does!) The best is to pick the one bundled with the image as a template.

If you want to pull a template from GitHub, do something like this:

➜ curl https://raw.githubusercontent.com/scylladb/scylla/master/conf/scylla.yaml -o scylla-template.yaml

If you instead want to pull a template from the container (recommended!), do something like this:

➜ docker run scylladb/scylla just-some-unrecognised-argument
➜ docker cp $(docker ps -lq):/etc/scylla/scylla.yaml scylla-template.yaml
➜ docker rm $(docker ps -lq)

Next we need to add some lines to the template in order to allow us to connect as an authenticated user and create keyspaces and such:

➜ cat >> ./scylla-template.yaml <<EOF

authenticator: 'com.scylladb.auth.TransitionalAuthenticator'
authorizer: 'com.scylladb.auth.TransitionalAuthorizer'
EOF

There are some network ports that are configurable as well:

  • A native transport port (without SSL): 9042 (default)
  • A native transport port (with SSL): 9142
  • An RPC listener port (Thrift): 9160
  • A REST API service port: 10000

The default super user is cassandra with password cassandra.

Start a three-node ScyllaDB cluster on the local machine for testing purposes

Node 1

Clone scylla-template.yaml for node 1.

➜ cp scylla-template.yaml scylla-node1.yaml

We want to run the first ScyllaDB instance in a container, exposing the internal native transport port 9042 available as 9042 on the host. I am mounting a local directory (~/scylla/mapped/node1) as a volume in the container, and also bind-mounting (overlaying) the external configuration file on top of the existing configuration file.

Currently, for the sake of this demo, I am only exposing the native transport port (9042) but the rest can be exposed as well.

➜ docker run --name scylla-node1 --publish 9042:9042 \
             --volume /Users/froran/scylla/mapped/node1:/var/lib/scylla \
             --volume /Users/froran/scylla/scylla-node1.yaml:/etc/scylla/scylla.yaml \
             --detach scylladb/scylla

In order to actually create a cluster of such nodes, subsequent nodes need to find this node (any node actually). The following command can be used to determine the IP-address of scylla-node1 in the docker environment.

➜ docker inspect --format='{{ .NetworkSettings.IPAddress }}' scylla-node1
172.17.0.2

Node 2

Clone scylla-template.yaml for node 2.

➜ cp scylla-template.yaml scylla-node2.yaml

We want to run the next (and second) ScyllaDB instance in a container, exposing the internal native transport port 9042 available as 9043 on the host. I am mounting a local directory (~/scylla/mapped/node2) as a volume in the container, and also bind-mounting (overlaying) the external configuration file on top of the existing configuration file.

➜ docker run --name scylla-node2 --publish 9043:9042 \
             --volume /Users/froran/scylla/mapped/node2:/var/lib/scylla \
             --volume /Users/froran/scylla/scylla-node2.yaml:/etc/scylla/scylla.yaml \
             --detach scylladb/scylla \
             --seeds="$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' scylla-node1)"

Node 3

Clone scylla-template.yaml for node 3.

➜ cp scylla-template.yaml scylla-node3.yaml

We want to run the next (and third) ScyllaDB instance in a container, exposing the internal native transport port 9042 available as 9044 on the host. I am mounting a local directory (~/scylla/mapped/node3) as a volume in the container, and also bind-mounting (overlaying) the external configuration file on top of the existing configuration file.

➜ docker run --name scylla-node3 --publish 9044:9042 \
             --volume /Users/froran/scylla/mapped/node3:/var/lib/scylla \
             --volume /Users/froran/scylla/scylla-node3.yaml:/etc/scylla/scylla.yaml \
             --detach scylladb/scylla \
             --seeds="$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' scylla-node1)"

Checking the cluster status

The cluster status can be queried by executing the nodetool in a running container, say in scylla-node1 (the first instance of ScyllaDB).

➜ docker exec -it scylla-node1 nodetool status demo
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                               Rack
UJ  172.17.0.3  ?          256          ?                 d0e2e9f6-3941-4ced-bda6-b1bbbe2c1c7f  rack1
UN  172.17.0.2  395.97 KB  256          100.0%            0cd8f34f-6988-4cae-b042-de98faac6482  rack1
UJ  172.17.0.4  ?          256          ?                 08c7cf41-59bd-4357-b279-0c491b252f21  rack1

So, the scylla-node2 and scylla-node3 nodes seem to be still joining the cluster -- wait and see :)

➜ docker exec -it scylla-node1 nodetool status demo
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns (effective)  Host ID                               Rack
UN  172.17.0.3  367.91 KB  256          62.9%             d0e2e9f6-3941-4ced-bda6-b1bbbe2c1c7f  rack1
UN  172.17.0.2  395.97 KB  256          67.2%             0cd8f34f-6988-4cae-b042-de98faac6482  rack1
UN  172.17.0.4  367.9 KB   256          69.9%             08c7cf41-59bd-4357-b279-0c491b252f21  rack1

Now scylla-node2 and scylla-node3 have successfully joined the cluster with scylla-node1.

Steps for reconfiguring a node in a running cluster

You may edit the configuration file of a cluster node either from the host or from within the container, but in any case you will have to restart the ScyllaDB instance.

For the sake of this demo, we will modify the configuration from within the container (from a Bash shell).

➜ docker exec -it scylla-node1 /bin/bash

[root@ae4179b857f0 /]# vi /etc/scylla/scylla.yaml
[root@ae4179b857f0 /]# exit

Restart ScyllaDB in node 1.

➜ docker exec -it scylla-node1 supervisorctl restart scylla
scylla: stopped
scylla: started

Creating a keyspace and a table

We will use cqlsh (the Cassandra Query Language Shell) to create a keyspace and a table, that we will later modify from our demo program.

➜ docker exec -it scylla-node1 cqlsh -ucassandra -pcassandra
Connected to  at 172.17.0.2:9042.
[cqlsh 5.0.1 | Cassandra 3.0.8 | CQL spec 3.3.1 | Native protocol v4]
Use HELP for help.
cassandra@cqlsh> LIST users;

 name      | super
-----------+-------
 cassandra |  True

(1 rows)

cassandra@cqlsh> CREATE KEYSPACE demo WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 2 } AND DURABLE_WRITES=true;

cassandra@cqlsh> DESCRIBE keyspaces;

system_traces  system_schema  system  demo

cassandra@cqlsh> USE demo;

cassandra@cqlsh:demo> CREATE TABLE IF NOT EXISTS contract (id INT PRIMARY KEY, code INT);

cassandra@cqlsh:demo> DESCRIBE contract;

CREATE TABLE demo.contract (
    id int PRIMARY KEY,
    code int
) WITH bloom_filter_fp_chance = 0.01
    AND caching = {'keys': 'ALL', 'rows_per_partition': 'ALL'}
    AND comment = ''
    AND compaction = {'class': 'SizeTieredCompactionStrategy'}
    AND compression = {}
    AND crc_check_chance = 1.0
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

cassandra@cqlsh:demo> SELECT * FROM contract;

 id | code
----+------

(0 rows)

cassandra@cqlsh:demo> INSERT INTO contract (id,code) VALUES (1, 42);

cassandra@cqlsh:demo> SELECT * FROM contract;

 id | code
----+------
  1 |   42

(1 rows)

cassandra@cqlsh:demo> exit

Connecting from a client

This simple demo program describes how to connect to the cluster and issue CQL statements from Java.

The demo program will just add lots of rows to the 'contract' table, almost 100.000 rows.

➜ docker exec -it scylla-node1 cqlsh -ucassandra -pcassandra
Connected to  at 172.17.0.2:9042.
[cqlsh 5.0.1 | Cassandra 3.0.8 | CQL spec 3.3.1 | Native protocol v4]
Use HELP for help.
cassandra@cqlsh> SELECT COUNT(*) FROM demo.contract;

 count
-------
 99999

(1 rows)
cassandra@cqlsh> exit

Stopping the cluster

First, we need to bring down the cluster nodes in an orderly fashion.

➜ docker exec -it scylla-node3 supervisorctl stop scylla
scylla: stopped
➜ docker exec -it scylla-node2 supervisorctl stop scylla
scylla: stopped
➜ docker exec -it scylla-node1 supervisorctl stop scylla
scylla: stopped

Next, the containers can be stopped and removed.

➜ docker ps --all
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                                                                  NAMES
e11d225bb296        scylladb/scylla     "/docker-entrypoint.…"   15 minutes ago      Up 15 minutes       7000-7001/tcp, 9160/tcp, 9180/tcp, 10000/tcp, 0.0.0.0:9044->9042/tcp   scylla-node3
e79f3d62d489        scylladb/scylla     "/docker-entrypoint.…"   17 minutes ago      Up 17 minutes       7000-7001/tcp, 9160/tcp, 9180/tcp, 10000/tcp, 0.0.0.0:9043->9042/tcp   scylla-node2
ae4179b857f0        scylladb/scylla     "/docker-entrypoint.…"   About an hour ago   Up About an hour    7000-7001/tcp, 9160/tcp, 9180/tcp, 10000/tcp, 0.0.0.0:9042->9042/tcp   scylla-node1

➜ docker stop e11d225bb296 e79f3d62d489 ae4179b857f0
➜ docker rm e11d225bb296 e79f3d62d489 ae4179b857f0