Top 30 OpenStack Interview Questions

Top 30 OpenStack Interview Questions: Here are the top interview questions of OpenStack. Be prepared for the interview. You can download the entire questions in a pdf format. so guys All the best for your interview.

1) Explain OpenStack.

OpenStack is an open source and free set of software tools or cloud computing platform which is used for managing and building cloud computing platform for private and public cloud.

OpenStack is referred as the future of Cloud Computing.


2) What are the modular architectural components of OpenStack?

Following is a list of OpenStack modular architectural components:

  • Dashboard
  • Compute
  • Networking
  • Object Storage
  • Block Storage
  • Identity service
  • Image Service
  • Telemetry
  • Orchestration
  • Database Service etc.

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3) What are the advantages/benefits of using OpenStack?

Advantages/Benefits of using OpenStack:

  • OpenStack can be used to develop any software as a service (SAAS) applications, for new developments or to improve existing solutions.
  • It can be used as a strong foundation to deliver self-service storage to IT users.
  • It provides easy to handle storage at lower costs.
  • It can deliver on-demand objective or block storage with higher scalability.
  • An enterprise can save a lot of licensing fees by switching virtual machines running on VMware to OpenStack.

4) What is “role” and “tenant” in OpenStack?

role: It specifies the authorization level of the user.

Tenant: It specifies a group of users.


5) What are the storage types allowed by OpenStack compute?

OpenStack supports two types of storage:

1. Persistent Storage or volume storage

2. Ephemeral Storage

Persistent Storage / Volume Storage: It is persistent and independent of any particular instance. This storage is created by users. There are three types of persistent storage:

  • Object storage: It is used to access binary objects through the REST API.
  • Block storage: It offers access-to-block storage devices by affixing volumes their current VM instances.
  • Shared File System storage: It provides a set of services to manage multiple files together for storage and exchange with multiple users at one time.

6) What are the two types of storage does OpenStack Compute provides?

OpenStack provides two classes of block storage,

  • Ephemeral Storage:  It is associated with a single unique instance. Based on the instance, the size is defined. When the instance associated with it is terminated, data on ephemeral storage ceases to exist
  • Volume Storage:   This storage is not dependent on any particular instance and is persistent.  Volumes are user created and within Quota

7) What are the basic functions of Identity Service in OpenStack?

Top 30 OpenStack Interview Questions The basic functions of Identity Service is

  • User Management:  It tracks the users and their permissions
  • Service Catalog: It provides a catalog of available services with their API endpoints

8) What are the main components of identity user management?

  • Users: It is a digital representation of a person, service or system who uses OpenStack cloud services
  • Tenants: A container used to group or isolate resource or identity objects.  Depending on service operator a tenant may map to a customer, account, organization or project
  • Roles:  A role includes a set of rights and privileges.  A role determines what operations a user is permitted to perform in a given tenant

9) Mention what are the networking options used in OpenStack?

The networking options used in OpenStack are

  • Flat Network Manager: IP addresses for VM instances are fetched from the subnet, and then injected into the image on launch
  • Flat DHCP Network Manager:  IP addresses for VM instances are fetched from the subnet specified by the network administrator
  • VLAN Network Manager: Compute creates a VLAN and bridge; DHCP server is started for each VLAN to pass out IP addresses to VM instances.

10) What is the meaning of term “Cinder” in OpenStack service?

For handling persistent storage for virtual machines, OpenStack provides the service referred to as Cinder. There are multiple backends for cinder.  The one that is utilized by default is LVM, called Cinder-Volumes.

11) How to get list of available Floating IPs from command line?

Available floating ips can be listed using the below command,

~]# openstack ip floating list | grep None | head -10

12) How to provision a virtual machine in specific availability zone and compute Host?

Top 30 OpenStack Interview Questions Let’s assume we want to provision a VM on the availability zone NonProduction in compute-02, use the beneath command to accomplish this,

~]# openstack server create --flavor m1.tiny --image cirros --nic net-id=e0be93b8-728b-4d4d-a272-7d672b2560a6 --security-group NonProd_SG  --key-name linuxtec --availability-zone NonProduction:compute-02  nonprod_testvm

13) How to get list of VMs which are provisioned on a specific Compute node?

Let’s assume we want to list the vms which are provisioned on compute-0-19, use below

Syntax: openstack server list –all-projects –long -c Name -c Host | grep -i  {Compute-Node-Name}

~# openstack server list --all-projects --long -c Name -c Host | grep -i  compute-0-19

14) How to view the console log of an openstack instance from command line?

Console logs of an instance can be viewed from the command line using the following commands,

First get the ID of an instance and then use the below command,

~# openstack console log show {Instance-id}

15) How to get console URL of an openstack instance?

Console URL of an instance can be retrieved from command line using the below openstack command,

~# openstack console url show {Instance-id}

16) Which hardware is required for networking in OpenStack?

In OpenStack,networking can be done with following hardware:

  • Networks
  • Routers
  • Subnets
  • Ports
  • Vendor Plugins

17) Which command is used to manage floating IP addresses in OpenStack?

nova floating-ip-*


18) Explain the usage of Cinder in OpenStack?

OpenStack Cinder is used to handle block storage in the context of OpenStack.


19) What is the use of $ nova floating-ip-pool-list command in OpenStack?

The $ nova floating-ip-pool-list command is used to list IP address information in OpenStack.


20) Explain the term “flavor” in OpenStack?

Top 30 OpenStack Interview Questions The term “flavor” is an available hardware configuration for a server, which defines the size of a virtual server that can be launched.

21) What is the command used for pause and unpause an instance?

  • To pause an instance, command used is $ nova pause INSTANCE_NAME
  • To unpause an instance, command used is $ nova unpause INSTANCE_NAME

22) What is the command used to list IP address information?

$ nova floating-ip-pool-list

23) What is the meaning of term “flavor” in OpenStack?

A flavour is an available hardware configuration for a server, which defines the size of a virtual server that can be launched.

24) What is the role of Tunnel Bridge (br-tun) on the compute node?

The tunnel bridge (br-tun) translates the VLAN tagged traffic from integration bridge to the tunnel ids using OpenFlow rules.

br-tun (tunnel bridge) allows the communication between the instances on different networks. Tunneling helps to encapsulate the traffic travelling over insecure networks, br-tun supports two overlay networks i.e GRE and VXLAN

25) What is the role of external OVS bridge (br-ex)?

Top 30 OpenStack Interview Questions As the name suggests this bridge forwards the traffic coming to and from the network to allow external access to instances. br-ex connects to the physical interface like eth2, so that floating IP traffic for tenants networks is received from the physical network and routed to the tenant network ports.

26) What is function of OpenFlow rules in OpenStack Networking?

OpenFlow rules is a mechanism that define how a packet will reach to destination starting from its source. OpenFlow rules resides in flow tables. The flow tables are part of OpenFlow switch.

When a packet arrives to a switch, it is processed by the first flow table, if it doesn’t match any flow entries in the table then packet is dropped or forwarded to another table.

27) How to display the information about a OpenFlow switch (like ports, no. of tables, no of buffer)?

Let’s assume we want to display the information about OpenFlow switch (br-int), run the following command,

[[email protected] ~]# ovs-ofctl show br-int
OFPT_FEATURES_REPLY (xid=0x2): dpid:0000fe981785c443
n_tables:254, n_buffers:256
capabilities: FLOW_STATS TABLE_STATS PORT_STATS QUEUE_STATS ARP_MATCH_IP
actions: output enqueue set_vlan_vid set_vlan_pcp strip_vlan mod_dl_src mod_dl_dst mod_nw_src mod_nw_dst mod_nw_tos mod_tp_src mod_tp_dst
 1(patch-tun): addr:3a:c6:4f:bd:3e:3b
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 2(qvob35d2d65-f3): addr:b2:83:c4:0b:42:3a
     config:     0
     state:      0
     current:    10GB-FD COPPER
     speed: 10000 Mbps now, 0 Mbps max
 ………………………………………

28) How to display the entries for all the flows in a switch?

Top 30 OpenStack Interview Questions Flows entries of a switch can be displayed using the command ‘ovs-ofctl dump-flows

Flows entries of a switch can be displayed using the command ‘ovs-ofctl dump-flows

Let’s assume we want to display flow entries of OVS integration bridge (br-int),

[[email protected] ~]# ovs-ofctl dump-flows br-int

29) What are Neutron Agents and how to list all neutron agents?

OpenStack neutron server acts as the centralized controller, the actual network configurations are executed either on compute and network nodes. Neutron agents are software entities that carry out configuration changes on compute or network nodes. Neutron agents communicate with the main neutron service via Neuron API and message queue.

Neutron agents can be listed using the following command,

~# openstack network agent list -c ‘Agent type’ -c Host -c Alive -c State

30) What is CPU pinning?

CPU pinning refers to reserving the physical cores for specific virtual machine. It is also known as CPU isolation or processor affinity. The configuration is in two parts:

  • it ensures that virtual machine can only run on dedicated cores
  • it also ensures that common host processes don’t run on those cores

In other words we can say pinning is one to one mapping of a physical core to a guest vCPU.