All the information about how to access a cloud provider and how to setup a cluster is stored in a configuration file. The default configuration file is stored in your home directory: ~/.elasticluster/config but you can specify a different location from the command line with the -c option.

If directory ~/.elasticluster/config.d exists (or, if you run elasticluster with option -c <PATH>, the directory <PATH>.d), all files named *.conf contained in that directory are read and parsed. In this way, you can handle multiple clusters easily by distributing the configuration over multiple files, and disable only some of them by renaming the files.

After installing ElastiCluster for the first time, we suggest you run the following command:

elasticluster list-templates

If no configuration file is found, it will copy an example configuration file in ~/.elasticluster/config. The example is fully commented and self-documenting.

However, the example configuration file is not complete, as it does not contain any authentication information, so you will get an error similar to the following:

WARNING:gc3.elasticluster:Deploying default configuration file to /home/antonio/.elasticluster/config.
WARNING:gc3.elasticluster:Ignoring Cluster `ipython`: required key not provided @ data['image_user']
WARNING:gc3.elasticluster:Ignoring cluster `ipython`.
Error validating configuration file '/home/antonio/.elasticluster/config': `required key not provided @ data['image_user']`

You will have to edit the configuration file in ~/.elasticluster/config and update it with the correct values.

Please refer to the following section to understand the syntax of the configuration file and to know which options you need to set in order to use elasticluster.

Basic syntax of the configuration file

The file is parsed by ConfigParser module and has a syntax similar to Microsoft Windows INI files.

It consists of sections led by a [sectiontype/name] header and followed by lines in the form:


Section names have the form [type/name] where type is one of:

define a cloud provider
define a way to access a virtual machine
define a way to setup the cluster
define the composition of a cluster. It contains references to the other sections.
override configuration for specific group of nodes within a cluster
usually not needed, allow to specify a custom path for the storage directory and the default storage type.

A valid configuration file must contain at least one section for each of the cloud, login, cluster, and setup sections.

Processing of configuration values

Within each key=value assignment, the value part undergoes the following transformations:

* References to enviromental variables of the form ``$VARNAME`` or

${VARNAME} are replaced by the content of the named environmental variable, wherever they appear in a value.

For instance, the following configuration snippet would set the OpenStack user name equal to the Linux user name on the computer where ElastiCluster is running:

username = $USER
# ...
  • The following special strings are substituted, wherever they appear in a value:

    this string ... ... expands to:
    ${elasticluster_playbooks} Path to the root directory containing the Ansible playbooks distributed with ElastiCluster
    ${ansible_pb_dir} Deprecated alias for ${elasticluster_playbooks}
  • Within values that name a file or path name, a ~ character at the beginning of the path name is substituted with the path to the user’s home directory. (In fact, this is a shorthand for $HOME/)

Cloud Section

A cloud section named <name> starts with:


The cloud section defines all properties needed to connect to a specific cloud provider.

You can define as many cloud sections you want, assuming you have access to different cloud providers and want to deploy different clusters in different clouds. The mapping between cluster and cloud provider is done in the cluster section (see later).

Currently three cloud providers are available:

  • openstack: supports OpenStack cloud
  • ec2_boto: supports Amazon EC2 and compatible cloud
  • google: supports Google Compute Engine

Therefore the following configuration option needs to be set in the cloud section:


the driver to use to connect to the cloud provider. ec2_boto, openstack or google

Valid configuration keys for ec2_boto


the url of the EC2 endpoint. For Amazon EC2 it is probably something like:

replace us-east-1 with the zone you want to use. If using OpenStack’s EC2 adapter, you can read the endpoint from the web interface


the access key (also known as access id) your cloud provider gave you to access its cloud resources.


the secret key (also known as secret id) your cloud provider gave you to access its cloud resources.


the availability zone you want to use.


the name or ID of the AWS Virtual Private Cloud to provision resources in.


request assignment of a floating IP when the instance is started. Valid values are True and False. Some cloud providers do not automatically assign a public IP to the instances, but this is often needed if you want to connect to the VM from outside. Setting request_floating_ip to True will force elasticluster to request such a floating IP if the instance doesn’t get one automatically.


If set to a non-zero value, ElastiCluster will allocate spot instances with a price less than or equal to the value given here. Note that there is currently no way to specify a currency: the amount is expressed in whatever currency is default in the Boto API (typically, US Dollars).

Defaults to 0, i.e., use regular non-spot instances.

This is typically best used in a compute node configuration section (see an example in the example configuration file); you probably do not want to run login, file server or similar central services on a spot instance (which can be terminated any time, depending on spot price bid).


Maximum amount of seconds to wait for a spot instance to become available; if a request for a spot instance cannot be satisfied in the given time, the instance startup process aborts. If set to 0 (default), then wait indefinitely.

Note: Ignored if price is zero (default).


Name of an IAM instance profile that contains roles allowing EC2 instances to have specified privileges. For example, you can allow EC2 instances to access S3 without passing credentials in.

Valid configuration keys for google


The API client id generated in the Google Developers Console


The API client secret generated in the Google Developers Console


The project id of your Google Compute Engine project


The GCE zone to be used. Default is us-central1-a.


The GCE network to be used. Default is default.

Valid configuration keys for openstack


The URL of the keystone service (main entry point for OpenStack clouds). If an environment variable OS_AUTH_URL is set when elasticluster starts, the config option will be ignored and the value of the variable will be used instead.


OpenStack username. If an environment variable OS_USERNAME is set when elasticluster starts, the config option will be ignored and the value of the variable will be used instead.


OpenStack password. If an environment variable OS_PASSWORD is set when elasticluster starts, the config option will be ignored and the value of the variable will be used instead.


OpenStack project to use (also known as tenant). If an environment variable OS_TENANT_NAME is set when elasticluster starts, the config option will be ignored and the value of the variable will be used instead.


OpenStack region (optional)


request assignment of a floating IP when the instance is started. Valid values: True, False. Some cloud providers does not automatically assign a public IP to the instances, but this is often needed if you want to connect to the VM from outside. Setting request_floating_ip to True will force elasticluster to request such a floating IP if the instance doesn’t get one automatically.


For instance, to connect to Amazon’s EC2 (region us-east-1) you can use:

ec2_access_key=****REPLACE WITH YOUR ACCESS ID****
ec2_secret_key=****REPLACE WITH YOUR SECRET KEY****

For Google Compute Engine you can use:

gce_client_id=****REPLACE WITH YOUR CLIENT ID****
gce_client_secret=****REPLACE WITH YOUR SECRET KEY****
gce_project_id=****REPLACE WITH YOUR PROJECT ID****

OpenStack users

From the horizon web interface you can download a file containing your EC2 credentials by logging into your provider web interface and clicking on:

=> “EC2 Credentials
=> “Download EC2 Credentials

The file will contain some values. Update the configuration file:

  • ec2_url using the value of the variable EC2_URL
  • ec2_access_key using the value of the variable EC2_ACCESS_KEY
  • ec2_secret_key using the value of the variable EC2_SECRET_KEY

Google Compute Engine users

To generate a client_id and client_secret to access the Google Compute Engine visit the following page:

  1. Select the project to be used for your cluster

  2. If a “Client ID for native application” is listed on this page, skip to step 8

  3. Under the OAuth section, click “Create new Client ID”

  4. Select “Installed Application”

  5. If prompted, click “Configure consent screen” and follow the instructions to set a “product name” to identify your Cloud project in the consent screen

  6. In the Create Client ID dialog, be sure the following are selected:

    Application type: Installed application
    Installed application type: Other
  7. Click the “Create Client ID” button

  8. You’ll see your Client ID and Client secret listed under “Client ID for native application”

Login Section

A login section named <name> starts with:


This section contains information on how to access the instances started on the cloud, including the user and the SSH keys to use.

Some of the values depend on the image you specified in the cluster section. Values defined here also can affect the setup section and the way the system is setup.

Mandatory configuration keys


the remote user you must use to connect to the virtual machine. In case you’re using Google Compute Engine you have to set your Google username here; so if your Gmail address is, your username is karl.marx


Can be True or False. True means that on the remote machine you can execute commands as root by running the sudo program.


the login name of the administrator. Use root unless you know what you are doing.


name of the keypair to use on the cloud provider. If the keypair does not exist it will be created by elasticluster.


file containing a valid RSA or DSA private key to be used to connect to the remote machine. Please note that this must match the user_key_public file (RSA and DSA keys go in pairs). Also note that Amazon does not accept DSA keys but only RSA ones.


file containing the RSA/DSA public key corresponding to the user_key_private private key. See user_key_private for more details.


For a typical Ubuntu machine, both on Amazon and most OpenStack providers, these values should be fine:


while for Hobbes appliances you will need to use the gc3-user instead:


Setup Section

A setup section named <name> starts with:


This section contain information on how to setup a cluster. After the cluster is started, elasticluster will run a setup provider in order to configure it.

General configuration keys


Type of the setup provider. So far, ansible is the only valid value (and, obviously, the default)

Ansible-specific mandatory configuration keys

The following configuration keys are only valid if provider is ansible.


Comma separated list of ansible groups the specific <class> will belong to. For each <class>_nodes in a [cluster/] section there should be a <class>_groups option to configure that specific class of nodes with the ansible groups specified.

If you are setting up a standard HPC cluster you probably want to have only two main groups: frontend_groups and compute_groups.

To configure a slurm cluster, for instance, you have the following available groups:

configure this machine as slurm masternode
compute nodes of a slurm cluster
configure as ganglia web frontend. On the master, you probably want to define ganglia monitor as well
configure as ganglia monitor.

You can combine more groups together, but of course not all combinations make sense. A common setup is, for instance:


This will configure the frontend node as slurm master and ganglia frontend, and the compute nodes as clients for both slurm and ganglia frontend.

A full list of the available groups is available at the Playbooks distributed with elasticluster page.


an entry of this type will define a variable called <varname> for the specific <class> and add it to the ansible inventory file. Please refer to the documentation of the playbook ot know which variables you can set and its meaning.


An entry of this type will define a variable called <varname> for all the nodes in the cluster, and add it to the ansible inventory file. Please refer to the documentation of the playbook ot know which variables you can set and its meaning.


Path to the playbook to use when configuring the system. The default value printed here points to the playbook distributed with elasticluster. The default value points to the playbooks distributed with elasticluster.


Path name of the ansible-playbook command; defaults to ansible-playbook, i.e., search for the command named ansible-playbook in the shell search path. Can also include arguments that will be prepended to other arguments that ElastiCluster adds to build the “setup” command invocation.


Arguments to append to the “setup” command invocation; can be used to override specific parameters or to further influence the behavior of the ansible-playbook command (e.g., skip certain tags).

The string is split according to POSIX shell parsing rules, so quotes can be used to protect arguments with embedded spaces.


# do not run any setup action tagged as 'users'
ansible_extra_args = --skip-tags users

# ask for confirmation at each step
ansible_extra_args = --step

Any configuration key starting with the string ansible_ is used to set the corresponding (uppercased) environmental variable and thus override Ansible configuration.

For example, the following settings raise the number of concurrent Ansible connections to 20 and allow a maximum waiting time of 300 seconds for a single task to finish:

# ...

The full list of environment variables used by Ansible is available from the Ansible configuration section of the Ansible online documentation. Invoking elasticluster setup with highest verbosity (e.g., -vvv) will dump the entire environment that Ansible is being called with to the DEBUG-level log.


Any ANSIBLE_* variables defined in the environment take precedence over what is defined in the [setup/*] section. Care must be taken when overriding some variables, particularly ANSIBLE_ROLES_PATH, which contain paths and references to parts of ElastiCluster: if those paths are missing from the replaced value, a number of fatal errors can happen.


Some (working) examples:




# Please note that this setup assumes you already have matlab
# installed on the image that is being used.

Cluster Section

A cluster section named <name> starts with:


The cluster section defines a template for a cluster. This section has references to each one of the other sections and define the image to use, the default number of compute nodes and the security group.

Mandatory configuration keys


the name of a valid cloud section. For instance hobbes or amazon-us-east-1


the name of a valid login section. For instance ubuntu or gc3-user


the name of a valid setup section. For instance, ansible-slurm or ansible-pbs


image id in ami format. If you are using OpenStack, you need to run euca-describe-images to get a valid ami-* id. With Google Compute Engine you can also use a URL of a private image. gcloud compute images describe <your_image_name> will show the selfLink URL to use.


the image type to use. Different cloud providers call it differently, could be instance type, instance size or flavor. This setting can be overwritten in the Cluster Node section, e.g. to use fewer resources on the frontend nodes than on the compute nodes.


Security group to use when starting the instance.


the number of nodes of type <class>. These configuration options will define the composition of your cluster. A very common configuration will include only two group of nodes:

the queue manager and frontend of the cluster. You probably want only one.
the worker nodes of the cluster.

Each <class>_nodes group is configured using the corresponding <class>_groups configuration option in the [setup/...] section.


ssh and sftp nodes will connect to only one node. This is the first of the group specified in this configuration option, or the first node of the first group in alphabetical order. For instance, if you don’t set any value for ssh_to and you defined two groups: frontend_nodes and compute_nodes, the ssh and sftp command will connect to compute001 which is the first compute_nodes node. If you specify frontend, instead, it will connect to frontend001 (or the first node of the frontend group).

Optional configuration keys


shell script to be executed (as root) when the machine starts. This is usually not needed because the ansible provider works on vanilla images, but if you are using other setup providers you may need to execute some command to bootstrap it.


comma separated list of network or subnet IDs the nodes of the cluster will be connected to. Only supported when the cloud provider is ec2_boto or openstack


Deprecated. Please rename to <class>_nodes_min.


Minimum amount of nodes of type <class> that must be up & running in order to start configuring the cluster. When starting a cluster, creation of some instances may fail; if at least this amount of nodes are started correctly (i.e. are not in error state), the cluster is configured anyway; otherwise, creation of the cluster will fail.


The maximum number of process to be created when virtual machines are started. Default is 10.
Define the type of boot disk to use. Only supported when the cloud provider is google. Supported values are pd-standard and pd-ssd. Default value is pd-standard.
Define the size of boot disk to use. Only supported when the cloud provider is google. Values are specified in gigabytes. Default value is 10.
Comma-separated list of instance tags. Only supported when the cloud provider is google.
Define the type of instance scheduling. Only supported when the cloud provider is google. Only supported value is preemptible.


Some (working) examples:

# Ubuntu image

# Use a different flavor on the compute nodes

# CentOS image

# ubuntu image


Cluster node section

A cluster node for the node type <nodetype> of the cluster <name> starts with:


This section allows you to override some configuration values for specific group of nodes. Assume you have a standard slurm cluster with a frontend which is used as manager node and nfs server for the home directories, and a set of compute nodes.

You may want to use different flavors for the frontend and the compute nodes, since for the first you need more space and you don’t need many cores or much memory, while the compute nodes may requires more memory and more cores but are not eager about disk space.

This is achieved defining, for instance, a bigdisk flavor (the name is just fictional) for the frontend and 8cpu32g for the compute nodes. Your configuration will thus look like:



Storage section

This section is used to customize the way elasticluster saves the state of your clusters on disk.

By default, all persistent data is saved in ~/.elasticluster/storage. This include two main files for each cluster:

  • <cluster>.yaml: a file containing information about your cluster
  • <cluster>.known_hosts: a file containing the ssh host keys of the nodes of your cluster.

These files are very important, since if they are broken or missing, elasticluster will not be able to recover any information about your cluster.

In addition to these two files, the setup provider and the cloud provider might create other files in the storage directory, but these are not critical, as they are re-genereted if needed.

To change the default path to the storage directory you can create a new storage section and set the storage_path value:

storage_path = /foo/bar

By default the status of the cluster is saved in YAML format, but also Pickle and Json formats are available. To save the cluster in a different fromat, add the option storage_type:

storage_type = json

Please note that only newly created storage will honour this option!