DCOS CLI for ArangoDB
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README.md

ArangoDB subcommand for DCOS

This repository contains a subcommand "arangodb" for the DCOS command line tool for Mesosphere clusters. It builds on top of the ArangoDB framework/service which can be found in

https://github.com/arangoDB/arangodb-mesos-framework

and which is distributed in binary form as a Docker image

arangodb/arangodb-mesos-framework

See the README.md in the framework repository for details on how the framework scheduler is configured.

Introduction

ArangoDB is a distributed, multi-model database featuring JSON documents, graphs and key/value pairs. It has a unifying query language that allows to mix all three data models and supports joins and transactions. As a distributed application, it is a very natural wish to be able to deploy an ArangoDB cluster easily on an Apache Mesos cluster, such that one can reap the benefits of better resource usage that Mesos promises, and run ArangoDB alongside other distributed applications. This framework makes this wish come true.

An ArangoDB cluster consists of different processes. As a central fault-tolerant configuration store we use etcd, we call these processes "agents" and the whole etcd-cluster "agency". Usually one will deploy three agents to allow for a failure (or indeed upgrade) of one of them without service interruption. The second type of processes are the "DBservers", which are ArangoDB instances that actually store data. No client should ever (need to) contact the DBservers directly. The third type of processes are the "coordinators". They are ArangoDB instances as well, they are the ones that receive client requests, export the usual ArangoDB HTTP/REST API, know the structure of the ArangoDB cluster (via the agency), and organise the distribution of the queries to the actual DBservers.

The user does not actually have to know much about this structure, however, since one can scale the coordinator layer independently from the DBserver layer, it is useful to understand this structure. As a rule of thumb, scale the DBserver layer up to get more storage space and scale the coordinator layer up if the bottleneck is CPU power for queries or Foxx apps (which run on the coordinators).

Prerequisites for Installation

This assumes that you have a working Mesosphere cluster and dcos command line utility. Note that you need at least Version 1.3 of DCOS because we need at least Version 0.23 of Apache Mesos to use the support for persistent volumes.

For deploying arangodb in a mesos-0.26 cluster and below you will have to create a separate role "arangodb" on the master so be sure to start your master with --roles=arangodb.

On mesosphere dcos edit /opt/mesosphere/etc/mesos-master and ensure the role is present:

MESOS_ROLES=slave_public,arangodb
MESOS_WEIGHTS=slave_public=1,arangodb=1

Make sure to restart the master so mesos knows about the new role.

ArangoDB needs an ETCD to store the configuration of the cluster. You can either use an existing ETCD cluster or ArangoDB will start a single ETCD instance for you.

ETCD configuration for production

In production it is recommended to use an ETCD cluster for resilience. In order to setup an ETCD cluster, you need to follow the instructions given in etcd-mesos. If you plan to use multiple ArangoDB clusters, you need to create an ETCD cluster with a unique name for each ArangoDB cluster.

For example, if you named your ETCD named etcd-arangodb, then use the ETCD service locator _etcd-server._client.etcd-arangodb.mesos. Before starting arangodb via the command line, create an options file options.json

{"arangodb":{"agency":"_etcd-server._client.etcd-arangodb.mesos"}}

and pass this file when starting

dcos package install arangodb --options=options.json

Installation/Startup

If you are using Mesos below 0.27, you are required to setup a special roles in the master. For 0.27 and above this is not necessary any more.

To create this separate role "arangodb" on the master, be sure to start your master with --roles=arangodb. On Mesosphere dcos edit /opt/mesosphere/etc/mesos-master and ensure the role is present:

MESOS_ROLES=slave_public,arangodb
MESOS_WEIGHTS=slave_public=1,arangodb=1

Make sure to restart the master so mesos knows about the new role.

Deploying an ArangoDB cluster is easy, just do:

dcos package update
dcos package install arangodb

This will install the dcos subcommand and start an instance of the ArangoDB framework/service under its standard name "arangodb" via Marathon. If you only want to install the command line tool, use

dcos package install --cli arangodb

For further configuration options using a JSON file see below in Section "Configuration options". In particular the needed resources and the size of the ArangoDB cluster can be configured in this way.

Deinstallation/Shutdown

To shutdown and delete your ArangoDB framework/service and to remove the command line tool, do the following two commands:

dcos arangodb uninstall ; dcos package uninstall arangodb

The first one uses the "arangodb" subcommand to gracefully shut down and delete all instances of your ArangoDB service. The framework scheduler itself will run in a silent mode for another 120 seconds. This enables the second command to remove the "arangodb" subcommand and the entry in Marathon that would otherwise restart the framework scheduler automatically.

Changing the ArangoDB cluster at runtime

This is not yet implemented. You will be able to scale up and down the ArangoDB cluster. The dcos subcommand will talk to the framework scheduler over its HTTP/REST API.

Service discovery with Mesos-DNS

All services started by the ArangoDB service are announced to Mesos and are thus available through Mesos-DNS, if you have it configured. The most important ones are the coordinators, which are the processes with which clients of the database cluster talk. The coordinators are called "coordinator1" to "coordinatorX" where "X" is replaced with the total number of coordinators. They all have a DNS entry in Mesos-DNS of the form

arangodb-coordinator1.arangodb.mesos

which points to an IP address that is valid within the Mesos cluster. If you need to contact them from the outside you need some IP forwarding rules. Furthermore, they all have an SRV record under a name like

_arangodb-coordinator1._tcp.arangodb.mesos

which contains a value like

0 0 1026 arangodb-coordinator1-s614f-s3.arangodb.mesos.

Here, the number 1026 is the port number under which the corresponding coordinator is reachable. There are similar entries for DBservers and agents but you should not need them at all. All interaction with the ArangoDB cluster goes via the coordinators.

Configuration options

There are a number of options, which can be specified in the following way:

dcos package install --config=<JSON_FILE> arangodb

where JSON_FILE is the path to a JSON file. For a list of possible attribute values and their documentation see

dcos package describe --config arangodb

Running more than one ArangoDB cluster on the same Mesosphere cluster

If you want to run more than one instance of the ArangoDB service on the same Mesosphere cluster, you have to specify --app-id <name> in the dcos package install command as well as the configuration option arangodb.id. They can be the same but need not be. Thus, start a new cluster with

dcos package install --config=myconfig.json --app-id=name1 arangodb

where myconfig.json is

{ "arangodb.id": "id1" }

Note the difference between "name1" and "id1"!

To destroy that cluster use

dcos arangodb uninstall --app-id id1 ; dcos package uninstall arangodb --app-id name1

After this the arangodb subcommand will also be uninstalled, to restore, do

dcos package install --cli arangodb

This will give you access to your other running ArangoDB clusters.

Ideally, the additional option should be unnecessary, but currently this trick is needed.

Running dcos within the internal network

The dcos sub-commands use the official hostname or IP. If you run dcos on a machine with an internal IP address and no access to the official IP, you can pass the --internal flag, for example

dcos arangodb webui --internal

Support and bug reports

The ArangoDB Mesos framework as well as the DCOS subcommand are supported by ArangoDB GmbH, the company behind ArangoDB. If you get stuck, need help or have questions, just ask via one of the following channels:

  • Google Group
  • hackers@arangodb.com: developer mailing list of ArangoDB
  • max@arangodb.com: direct email to Max Neunhöffer
  • frank@arangodb.com: direct email to Frank Celler
  • mop@arangodb.com: direct email to Andreas Streichardt

Additionally, we track issues, bug reports and questions via the github issue trackers at