OpenReplica provides easily launch for concoord on remote machines, and it is especially built to launch concoord instances on Amazon EC2 servers easily. In this section we cover how you can setup a set of machines and launch concoord remotely using OpenReplica.
You can easily launch your EC2 instances using the web interface provided by Amazon AWS. In this example we launch an instance running 64-bit Amazon Linux. Before you launch your instance, you will have to create a keypair to login to your instances, make sure to keep your private key safe. The best way is to move your key-pair to the .ssh directory once you download the [my-key-pair].pem file:
$ mv [my-key-pair].pem ~/.ssh/
$ ssh-add ~/.ssh/[my-key-pair].pem
Once you did these, now is the time to connect to your instance:
$ ssh -i [my-key-pair].pem ec2-user@[public_dns_name]
After this point on, you should be able to connect to your instance without explicitly passing the key as a parameter, as follows:
$ ssh ec2-user@[public_dns_name]
To enable execution of remote sudo commands SSH into your instance and run:
$ sudo visudo
In the file that opens find the line Defaults requiretty and add line Defaults:ec2-user !requiretty below it. Save the file and exit. The file opens with the vi editor. If you are not familiar with vi commands, to insert new text press i to go into insert mode and add the new line. After you are done, press ESC and ZZ to save and exit.
At this point, your EC2 instance should be easily accessible.
Using OpenReplica developers can configure and remotely launch ConCoord instances on remote machines easily. Firstly, OpenReplica keeps the configuration information of machines that will be running the ConCoord instance. Secondly, using ConCoord developers can easily start replica and nameserver nodes on the machines that are added to the configuration. And lastly, using OpenReplica developers can easily manage EC2 instances.
Like ConCoord, OpenReplica can be used as a commandline script. It supports the following commands:
openreplica config - prints config file openreplica addsshkey [sshkeyfilename] - adds sshkey filename to config openreplica addusername [ssh username] - adds ssh username to config openreplica addnode [publicdns] - adds public dns for node to config openreplica setup [publicdns] - downloads and sets up concoord on the given node openreplica replica [concoord arguments] - starts a replica node on EC2 openreplica nameserver [concoord arguments] - starts a nameserver node on EC2
To use OpenReplica, you should first register the nodes you want to use. To register nodes, you will need the filename of the sshkey you use to ssh into these nodes, as well as the username.
To add the sshkey:
$ openreplica addsshkey [my-key-pair].pem
To add the username:
$ openreplica addusername ec2-user
To add a node:
$ openreplica addnode [public_dns_name]
When adding nodes to OpenReplica, it automatically checks the nodes for eligibility to run ConCoord and warns the user if an update or change is required. Similarly, if ConCoord cannot connect to the node, it lets the user know.
$ openreplica addsshkey concoord.pem
Adding SSHKEY to CONFIG: concoord.pem
$ openreplica addusername ec2-user
Adding USERNAME to CONFIG: ec2-user
$ openreplica addnode ec2-54-186-26-155.us-west-2.compute.amazonaws.com
Adding NODE to CONFIG: ec2-54-186-26-155.us-west-2.compute.amazonaws.com
Cannot connect to node, check if it is up and running.
Once OpenReplica is set up, nodes can be started as if they are being started on the local machine.
To start a bootstrap replica node that doesn’t need to be connected to another replica:
$ openreplica replica -o concoord.object.counter.Counter -a 127.0.0.1 -p 14000
To start replica nodes to join an active ConCoord instance:
$ openreplica replica -o concoord.object.counter.Counter -b 127.0.0.1:14000 -a 127.0.0.1 -p 14001
The nodes can also be run in the debug mode or with a logger with the commands shown below:
Usage: openreplica replica [-h] [-a ADDR] [-p PORT] [-b BOOTSTRAP] [-o OBJECTNAME] [-l LOGGER] [-n DOMAIN] [-r] [-w] [-d]
-h, --help show this help message and exit
-a ADDR, --addr ADDR address for the node
-p PORT, --port PORT port for the node
-b BOOTSTRAP, --boot BOOTSTRAP address:port tuple for the bootstrap peer
-o OBJECTNAME, --objectname OBJECTNAME client object dotted name
-l LOGGER, --logger LOGGER logger address
-n DOMAIN, --domainname DOMAIN domain name that the name server will accept queries for
-r, --route53 use Route53
-w, --writetodisk writing to disk on/off
-d, --debug debug on/off
You can dynamically locate nodes in a given ConCoord instance using DNS queries if the instance includes replicas that can act as name servers. There are two ways you can run a ConCoord Replica as a name server.
To use a replica node as a master name server first you have to setup the name server delegations (you can do this by updating the domain name server information of any domain name you own from the domain registrar you use (godaddy, namecheap etc.)). Once all the delegations are setup for the ip address the replica uses, you can start a replica node as a name server for counterdomain.com as follows:
$ openreplica replica -o concoord.object.counter.Counter -a 127.0.0.1 -n counterdomain.com
And to start the replica to join an already running ConCoord instance, provide the bootstrap:
$ openreplica replica -o concoord.object.counter.Counter -a 127.0.0.1 -b 127.0.0.1:14000 -n counterdomain.com
When the replica starts running, you can send queries for counterdomain.com and see the most current set of nodes as follows:
$ dig -t a counterdomain.com # returns set of Replicas
$ dig -t srv _concoord._tcp.counterdomain.com # returns set of Replicas with ports
$ dig -t txt counterdomain.com # returns set of all nodes
$ dig -t ns counterdomain.com # returns set of name servers
First make sure that boto is installed on the machine you want to run the Route53 name server. OpenReplica tries to do this automatically when a replica is run as a Route53 name server, but if it fails to do so, you can easily install boto on the machine you want as follows:
$ pip install boto
Before starting a name server connected to Amazon Route53, you should have a Route53 account set up and ready to receive requests. This is done through the AWS Console (http://console.aws.amazon.com/route53), by creating a new Hosted Zone to host your domain name.
After your Route53 account is set up, the name server can update Route53 records every time the view of the system changes.
To use the Name Server to update Amazon Route53, you should provide your AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY. You can retrieve these from the AWS Console (http://console.aws.amazon.com/iam/), by looking under the security credentials of the username that you used while creating the Hosted Zone for your domain name. Once you have the information, you can set up Route53 configuration easily as follows:
$ openreplica route53 [public_dns AWS_ACCESS_KEY_ID AWS_SECRET_ACCESS_KEY]
Once you make sure that your Route53 account is set up and the configuration file includes your AWS credentials, you can start the replica with a name server as follows:
$ openreplica replica -o concoord.object.counter.Counter -n counterdomain.com -r
When the replica starts running, you can send queries for counterdomain.com and see the most current set of nodes as follows:
$ dig -t a counterdomain.com # returns set of Replicas
$ dig -t srv _concoord._tcp.counterdomain.com # returns set of Replicas with ports
$ dig -t txt counterdomain.com # returns set of all nodes
$ dig -t ns counterdomain.com # returns set of name servers