This guide addresses specific aspects of Sahara configuration that pertain to advanced usage. It is divided into sections about various features that can be utilized, and their related configurations.
Sahara accesses instances at several stages of cluster spawning through SSH and HTTP. Floating IPs and network namespaces (see Networking configuration) will be automatically used for access when present. When floating IPs are not assigned to instances and namespaces are not being used, sahara will need an alternative method to reach them.
The proxy_command parameter of the configuration file can be used to give sahara a command to access instances. This command is run on the sahara host and must open a netcat socket to the instance destination port. The {host} and {port} keywords should be used to describe the destination, they will be substituted at runtime. Other keywords that can be used are: {tenant_id}, {network_id} and {router_id}.
For example, the following parameter in the sahara configuration file would be used if instances are accessed through a relay machine:
[DEFAULT]
proxy_command='ssh relay-machine-{tenant_id} nc {host} {port}'
Whereas the following shows an example of accessing instances though a custom network namespace:
[DEFAULT]
proxy_command='ip netns exec ns_for_{network_id} nc {host} {port}'
Hadoop provides the data-locality feature to enable task tracker and data nodes the capability of spawning on the same rack, Compute node, or virtual machine. Sahara exposes this functionality to the user through a few configuration parameters and user defined topology files.
To enable data-locality, set the enable_data_locality parameter to True in the sahara configuration file
[DEFAULT]
enable_data_locality=True
With data locality enabled, you must now specify the topology files for the Compute and Object Storage services. These files are specified in the sahara configuration file as follows:
[DEFAULT]
compute_topology_file=/etc/sahara/compute.topology
swift_topology_file=/etc/sahara/swift.topology
The compute_topology_file should contain mappings between Compute nodes and racks in the following format:
compute1 /rack1
compute1 /rack2
compute1 /rack2
Note that the Compute node names must be exactly the same as configured in OpenStack (host column in admin list for instances).
The swift_topology_file should contain mappings between Object Storage nodes and racks in the following format:
node1 /rack1
node2 /rack2
node3 /rack2
Note that the Object Storage node names must be exactly the same as configured in the object ring. Also, you should ensure that instances with the task tracker process have direct access to the Object Storage nodes.
Hadoop versions after 1.2.0 support four-layer topology (for more detail please see HADOOP-8468 JIRA issue). To enable this feature set the enable_hypervisor_awareness parameter to True in the configuration file. In this case sahara will add the Compute node ID as a second level of topology for virtual machines.
Sahara can be configured to run in a distributed mode that creates a separation between the API and engine processes. This allows the API process to remain relatively free to handle requests while offloading intensive tasks to the engine processes.
The sahara-api application works as a front-end and serves user requests. It offloads ‘heavy’ tasks to the sahara-engine process via RPC mechanisms. While the sahara-engine process could be loaded with tasks, sahara-api stays free and hence may quickly respond to user queries.
If sahara runs on several hosts, the API requests could be balanced between several sahara-api hosts using a load balancer. It is not required to balance load between different sahara-engine hosts as this will be automatically done via the message broker.
If a single host becomes unavailable, other hosts will continue serving user requests. Hence, a better scalability is achieved and some fault tolerance as well. Note that distributed mode is not a true high availability. While the failure of a single host does not affect the work of the others, all of the operations running on the failed host will stop. For example, if a cluster scaling is interrupted, the cluster will be stuck in a half-scaled state. The cluster might continue working, but it will be impossible to scale it further or run jobs on it via EDP.
To run sahara in distributed mode pick several hosts on which you want to run sahara services and follow these steps:
On each host install and configure sahara using the installation guide except:
- Do not run sahara-db-manage or launch sahara with sahara-all
- Ensure that each configuration file provides a database connection string to a single database for all hosts.
Run sahara-db-manage as described in the installation guide, but only on a single (arbitrarily picked) host.
The sahara-api and sahara-engine processes use oslo.messaging to communicate with each other. You will need to configure it properly on each host (see below).
Run sahara-api and sahara-engine on the desired hosts. You may run both processes on the same or separate hosts as long as they are configured to use the same message broker and database.
To configure oslo.messaging, first you will need to choose a message broker driver. Currently there are three drivers provided: RabbitMQ, Qpid or ZeroMQ. For the RabbitMQ or Qpid drivers please see the Notifications configuration documentation for an explanation of common configuration options.
For an expanded view of all the options provided by each message broker driver in oslo.messaging please refer to the options available in the respective source trees:
- For Rabbit MQ see
- rabbit_opts variable in impl_rabbit.py
- amqp_opts variable in amqp.py
- For Qpid see
- qpid_opts variable in impl_qpid.py
- amqp_opts variable in amqp.py
- For Zmq see
- zmq_opts variable in impl_zmq.py
- matchmaker_opts variable in matchmaker.py
- matchmaker_redis_opts variable in matchmaker_redis.py
- matchmaker_opts variable in matchmaker_ring.py
These options will also be present in the generated sample configuration file. For instructions on creating the configuration file please see the Sahara Configuration Guide.
Sahara generates and stores several passwords during the course of operation. To harden sahara’s usage of passwords it can be instructed to use an external key manager for storage and retrieval of these secrets. To enable this feature there must first be an OpenStack Key Manager service deployed within the stack. Currently, the barbican project is the only key manager supported by sahara.
With a Key Manager service deployed on the stack, sahara must be configured to enable the external storage of secrets. This is accomplished by editing the sahara configuration file as follows:
[DEFAULT]
use_external_key_manager=True
Additionally, at this time there are two more values which must be provided to ensure proper access for sahara to the Key Manager service. These are the Identity domain for the administrative user and the domain for the administrative project. By default these values will appear as:
[DEFAULT]
admin_user_domain_name=default
admin_project_domain_name=default
With all of these values configured and the Key Manager service deployed, sahara will begin storing its secrets in the external manager.
Warning
The indirect VMs access feature is in alpha state. We do not recommend using it in a production environment.
Sahara needs to access instances through SSH during cluster setup. This access can be obtained a number of different ways (see Networking configuration, Floating IP management, Custom network topologies). Sometimes it is impossible to provide access to all nodes (because of limited numbers of floating IPs or security policies). In these cases access can be gained using other nodes of the cluster as proxy gateways. To enable this set is_proxy_gateway=True for the node group you want to use as proxy. Sahara will communicate with all other cluster instances through the instances of this node group.
Note, if use_floating_ips=true and the cluster contains a node group with is_proxy_gateway=True, the requirement to have floating_ip_pool specified is applied only to the proxy node group. Other instances will be accessed through proxy instances using the standard private network.
Note, the Cloudera Hadoop plugin doesn’t support access to Cloudera manager through a proxy node. This means that for CDH clusters only nodes with the Cloudera manager can be designated as proxy gateway nodes.
Sahara supports multi region deployment. To enable this option each instance of sahara should have the os_region_name=<region> parameter set in the configuration file. The following example demonstrates configuring sahara to use the RegionOne region:
[DEFAULT]
os_region_name=RegionOne
In cases where a proxy command is being used to access cluster instances (for example, when using namespaces or when specifying a custom proxy command), rootwrap functionality is provided to allow users other than root access to the needed operating system facilities. To use rootwrap the following configuration parameter is required to be set:
[DEFAULT]
use_rootwrap=True
Assuming you elect to leverage the default rootwrap command (sahara-rootwrap), you will need to perform the following additional setup steps:
sahara ALL = (root) NOPASSWD: /usr/bin/sahara-rootwrap /etc/sahara/rootwrap.conf *
[Filters]
ip: IpNetnsExecFilter, ip, root
nc: CommandFilter, nc, root
kill: CommandFilter, kill, root
If you wish to use a rootwrap command other than sahara-rootwrap you can set the following parameter in your sahara configuration file:
[DEFAULT]
rootwrap_command='sudo sahara-rootwrap /etc/sahara/rootwrap.conf'
For more information on rootwrap please refer to the official Rootwrap documentation
To improve security for clusters accessing files in Object Storage, sahara can be configured to use proxy users and delegated trusts for access. This behavior has been implemented to reduce the need for storing and distributing user credentials.
The use of proxy users involves creating an Identity domain that will be designated as the home for these users. Proxy users will be created on demand by sahara and will only exist during a job execution which requires Object Storage access. The domain created for the proxy users must be backed by a driver that allows sahara’s admin user to create new user accounts. This new domain should contain no roles, to limit the potential access of a proxy user.
Once the domain has been created, sahara must be configured to use it by adding the domain name and any potential delegated roles that must be used for Object Storage access to the sahara configuration file. With the domain enabled in sahara, users will no longer be required to enter credentials for their data sources and job binaries referenced in Object Storage.
First a domain must be created in the Identity service to hold proxy users created by sahara. This domain must have an identity backend driver that allows for sahara to create new users. The default SQL engine is sufficient but if your keystone identity is backed by LDAP or similar then domain specific configurations should be used to ensure sahara’s access. Please see the Keystone documentation for more information.
With the domain created, sahara’s configuration file should be updated to include the new domain name and any potential roles that will be needed. For this example let’s assume that the name of the proxy domain is sahara_proxy and the roles needed by proxy users will be Member and SwiftUser.
[DEFAULT]
use_domain_for_proxy_users=True
proxy_user_domain_name=sahara_proxy
proxy_user_role_names=Member,SwiftUser
A note on the use of roles. In the context of the proxy user, any roles specified here are roles intended to be delegated to the proxy user from the user with access to Object Storage. More specifically, any roles that are required for Object Storage access by the project owning the object store must be delegated to the proxy user for authentication to be successful.
Finally, the stack administrator must ensure that images registered with sahara have the latest version of the Hadoop swift filesystem plugin installed. The sources for this plugin can be found in the sahara extra repository. For more information on images or swift integration see the sahara documentation sections Building Images for Vanilla Plugin and Swift Integration.
The Block Storage service provides the ability to define volume instance locality to ensure that instance volumes are created on the same host as the hypervisor. The InstanceLocalityFilter provides the mechanism for the selection of a storage provider located on the same physical host as an instance.
To enable this functionality for instances of a specific node group, the volume_local_to_instance field in the node group template should be set to True and some extra configurations are needed:
The cinder-volume service should be launched on every physical host and at least one physical host should run both cinder-scheduler and cinder-volume services.
InstanceLocalityFilter should be added to the list of default filters (scheduler_default_filters in cinder) for the Block Storage configuration.
The Extended Server Attributes extension needs to be active in the Compute service (this is true by default in nova), so that the OS-EXT-SRV-ATTR:host property is returned when requesting instance info.
The user making the call needs to have sufficient rights for the property to be returned by the Compute service. This can be done by:
by changing nova’s policy.json to allow the user access to the extended_server_attributes option.
by designating an account with privileged rights in the cinder configuration:
os_privileged_user_name =
os_privileged_user_password =
os_privileged_user_tenant =
It should be noted that in a situation when the host has no space for volume creation, the created volume will have an Error state and can not be used.