[openstack-dev] Disaster Recovery for OpenStack - call for stakeholder - discussion reminder

Deepak Shetty dpkshetty at gmail.com
Thu Mar 20 06:54:01 UTC 2014

Hi List,
    I was looking at the etherpad and March 19 notes and have few Qs

1) How is the "DR middleware" (depicted in Ron's youtube video) different
than the "replication agent" (noted in the March 19 etherpad notes). Are
they same, if not, how/why are they different ?

2) Maybe a dumb Q.. but still.. Why do we need to worry about syncing
metadata differently ? If all the storage that is used across openstack
services (and in typical case it might be just 1 backend, say GlsuterFS)
are beign replicated durign the DR, wouldn't the metadata be replicated
too.. why do we need to be concerned abt it as a separate entity ?


On Wed, Mar 19, 2014 at 2:11 PM, Ronen Kat <RONENKAT at il.ibm.com> wrote:

> For those who are interested we will discuss the disaster recovery
> use-cases and how to proceed toward the Juno summit on March 19 at 17:00
> UTC (invitation below)
> Call-in:
> *https://www.teleconference.att.com/servlet/glbAccess?process=1&accessCode=6406941&accessNumber=1809417783#C2*<https://www.teleconference.att.com/servlet/glbAccess?process=1&accessCode=6406941&accessNumber=1809417783#C2>
> Passcode: 6406941
> Etherpad:
> https://etherpad.openstack.org/p/juno-disaster-recovery-call-for-stakeholders
> Wiki: https://wiki.openstack.org/wiki/DisasterRecovery
> Regards,
> __________________________________________
> Ronen I. Kat, PhD
> Storage Research
> *IBM Research - Haifa*
> Phone: +972.3.7689493
> Email: ronenkat at il.ibm.com
> From:        "Luohao (brian)" <brian.luohao at huawei.com>
> To:        "OpenStack Development Mailing List (not for usage questions)"
> <openstack-dev at lists.openstack.org>,
> Date:        14/03/2014 03:59 AM
> Subject:        Re: [openstack-dev] Disaster Recovery for OpenStack -
> call for stakeholder
> ------------------------------
> 1.  fsfreeze with vss has been added to qemu upstream, see
> http://lists.gnu.org/archive/html/qemu-devel/2013-02/msg01963.html for
> usage.
> 2.  libvirt allows a client to send any commands to qemu-ga, see
> http://wiki.libvirt.org/page/Qemu_guest_agent
> 3.  linux fsfreeze is not equivalent to windows fsfreeze+vss. Linux
> fsreeze offers fs consistency only, while windows vss allows agents like
> sqlserver to register their plugins to flush their cache to disk when a
> snapshot occurs.
> 4.  my understanding is xenserver does not support fsfreeze+vss now,
> because xenserver normally does not use block backend in qemu.
> -----Original Message-----
> From: Bruce Montague [mailto:Bruce_Montague at symantec.com<Bruce_Montague at symantec.com>]
> Sent: Thursday, March 13, 2014 10:35 PM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] Disaster Recovery for OpenStack - call for
> stakeholder
> Hi, about OpenStack and VSS. Does anyone have experience with the qemu
> project's implementation of VSS support? They appear to have a within-guest
> agent, qemu-ga, that perhaps can work as a VSS requestor. Does it also work
> with KVM? Does qemu-ga work with libvirt (can VSS quiesce be triggered via
> libvirt)? I think there was an effort for qemu-ga to use fsfreeze as an
> equivalent to VSS on Linux systems, was that done?  If so, could an
> OpenStack API provide a generic quiesce request that would then get passed
> to libvirt? (Also, the XenServer VSS support seems different than
> qemu/KVM's, is this true? Can it also be accessed through libvirt?
> Thanks,
> -bruce
> -----Original Message-----
> From: Alessandro Pilotti [mailto:apilotti at cloudbasesolutions.com<apilotti at cloudbasesolutions.com>
> ]
> Sent: Thursday, March 13, 2014 6:49 AM
> To: openstack-dev at lists.openstack.org
> Subject: Re: [openstack-dev] Disaster Recovery for OpenStack - call for
> stakeholder
> Those use cases are very important in enterprise scenarios requirements,
> but there's an important missing piece in the current OpenStack APIs:
> support for application consistent backups via Volume Shadow Copy (or other
> solutions) at the instance level, including differential / incremental
> backups.
> VSS can be seamlessly added to the Nova Hyper-V driver (it's included with
> the free Hyper-V Server) with e.g. vSphere and XenServer supporting it as
> well (quescing) and with the option for third party vendors to add drivers
> for their solutions.
> A generic Nova backup / restore API supporting those features is quite
> straightforward to design. The main question at this stage is if the
> OpenStack community wants to support those use cases or not. Cinder
> backup/restore support [1] and volume replication [2] are surely a great
> starting point in this direction.
> Alessandro
> [1] https://review.openstack.org/#/c/69351/
> [2] https://review.openstack.org/#/c/64026/
> > On 12/mar/2014, at 20:45, "Bruce Montague" <Bruce_Montague at symantec.com>
> wrote:
> >
> >
> > Hi, regarding the call to create a list of disaster recovery (DR) use
> cases (
> http://lists.openstack.org/pipermail/openstack-dev/2014-March/028859.html), the following list sketches some speculative OpenStack DR use cases.
> These use cases do not reflect any specific product behavior and span a
> wide spectrum. This list is not a proposal, it is intended primarily to
> solicit additional discussion. The first basic use case, (1), is described
> in a bit more detail than the others; many of the others are elaborations
> on this basic theme.
> >
> >
> >
> > * (1) [Single VM]
> >
> > A single Windows VM with 4 volumes and VSS (Microsoft's Volume
> Shadowcopy Services) installed runs a key application and integral
> database. VSS can quiesce the app, database, filesystem, and I/O on demand
> and can be invoked external to the guest.
> >
> >   a. The VM's volumes, including the boot volume, are replicated to a
> remote DR site (another OpenStack deployment).
> >
> >   b. Some form of replicated VM or VM metadata exists at the remote
> site. This VM/description includes the replicated volumes. Some systems
> might use cold migration or some form of wide-area live VM migration to
> establish this remote site VM/description.
> >
> >   c. When specified by an SLA or policy, VSS is invoked, putting the
> VM's volumes in an application-consistent state. This state is flushed all
> the way through to the remote volumes. As each remote volume reaches its
> application-consistent state, this is recognized in some fashion, perhaps
> by an in-band signal, and a snapshot of the volume is made at the remote
> site. Volume replication is re-enabled immediately following the snapshot.
> A backup is then made of the snapshot on the remote site. At the completion
> of this cycle, application-consistent volume snapshots and backups exist on
> the remote site.
> >
> >   d.  When a disaster or firedrill happens, the replication network
> > connection is cut. The remote site VM pre-created or defined so as to
> use the replicated volumes is then booted, using the latest
> application-consistent state of the replicated volumes. The entire VM
> environment (management accounts, networking, external firewalling, console
> access, etc..), similar to that of the primary, either needs to pre-exist
> in some fashion on the secondary or be created dynamically by the DR
> system. The booting VM either needs to attach to a virtual network
> environment similar to at the primary site or the VM needs to have boot
> code that can alter its network personality. Networking configuration may
> occur in conjunction with an update to DNS and other networking
> infrastructure. It is necessary for all required networking configuration
>  to be pre-specified or done automatically. No manual admin activity should
> be required. Environment requirements may be stored in a DR configuration o
> r database associated with the replication.
> >
> >   e. In a firedrill or test, the virtual network environment at the
> remote site may be a "test bubble" isolated from the real network, with
> some provision for protected access (such as NAT). Automatic testing is
> necessary to verify that replication succeeded. These tests need to be
> configurable by the end-user and admin and integrated with DR orchestration.
> >
> >   f. After the VM has booted and been operational, the network
> > connection between the two sites is re-established. A replication
> > connection between the replicated volumes is restablished, and the
> > replicated volumes are re-synced, with the roles of primary and
> > secondary reversed. (Ongoing replication in this configuration may
> > occur, driven from the new primary.)
> >
> >   g. A planned failback of the VM to the old primary proceeds similar to
> the failover from the old primary to the old replica, but with roles
> reversed and the process minimizing offline time and data loss.
> >
> >
> >
> > * (2) [Core tenant/project infrastructure VMs]
> >
> > Twenty VMs power the core infrastructure of a group using a private
> cloud (OpenStack in their own datacenter). Not all VMs run Windows with
> VSS, some run Linux with some equivalent mechanism, such as qemu-ga,
> driving fsfreeze and signal scripts. These VMs are replicated to a remote
> OpenStack deployment, in a fashion similar to (1). Orchestration occurring
> at the remote site on failover is more complex (correct VM boot order is
> orchestrated, DHCP service is configured as expected, all IPs are made
> available and verified). An equivalent virtual network topology consisting
> of multiple networks or subnets might be pre-created or dynamically created
> at failover time.
> >
> >   a. Storage for all volumes of all VMs might be on a single storage
> backend (logically a single large volume containing many smaller
> sub-volumes, examples being a VMware datastore or Hyper-V CSV). This entire
> large volume might be replicated between similar storage backends at the
> primary and secondary site. A single replicated large volume thus
> replicates all the tenant VM's volumes. The DR system must trigger quiesce
> of all volumes to application-consistent state.
> >
> >   b. This environment needs to deal with failures of the primary
> datacenter (as when a trenching tool cuts its connection to the internet),
> routine firedrill tests that perform failover and failback, and planned
> migration.
> >
> >   c. VSS or fsfreeze may be expected to fail for some VMs and policies
> and SLAs need to contend with this and alert admins for manual follow-up.
> >
> >   d. Network bandwidth used for replication needs to be throttled so as
> not to overly disrupt the private cloud's gateway capacity.
> >
> >   e. DR replication needs to deal with intermittent network replication
> failure and recover gracefully. In case of a known network issue, such as
> maintenance, it needs to be possible for the admin to explicitly suspend
> network replication. Replication I/O is then logged locally at the primary
> site in some fashion. The remote site needs to stay replication ready, but
> failover does not occur. When the network issue is over, replication
> resumes, perhaps recovering via a log, a map of updated blocks, or an
> equivalent technique. In this example the RPO window is deliberately
> ignored and allowed to grow until replication is resumed by the admin.
> >
> >   f. This tenant requires encryption of network replication traffic.
> >
> >   g. Cost accounting and chargeback is required.
> >
> >
> >
> > * (3) [Multi-tier app infrastructure]
> >
> > A tenant has a service consisting of 8 multi-tier apps that each consist
> of 3 to 5 VMs, with each VM having 2 to 4 disks. Replication snapshots need
> to be made of the volumes in an application-consistent way across all the
> volumes of all the VMs in all the multi-tier apps. Again, these volumes may
> exist on a single large volume or datastore, perhaps simplifying creation
> of the cross-VM application consistency snapshot. Not all of the VMs in a
> multi-tier app may need to be quiesced, some may be stateless and simply
> need to be recovered to a running state.
> >
> > a. This tenant requires that 3 of the multi-tier apps failover to one
> remote OpenStack site and the other 5 multi-tier apps failover to a
> different remote site than the first.
> >
> > b. This tenant weekly performs a non-disruptive test-bubble failover
> test. Real failover is not triggered. Instead, all the multi-tier app VMs
> that would boot upon failure are booted (from their latest snapshots on the
> secondary), but the VM's virtual network environment on the secondary is
> isolated from external networking. Test bubbles at the two OpenStack remote
> sites may need to be connected via some VPN/tunnel or equivalent without
> manual admin activity.
> >
> >
> >
> > * (4) [Tenant failover]
> >
> > An OpenStack tenant has 40 VMs, relatively lightly loaded, used for
> development. The VMs do not contain VSS, qemu-ga, or standard tools (they
> may be running any Linux distro, some may be running Plan9, the tenant may
> be doing Linux kernel development (that is, the VMs can be anything)). A
> remote OpenStack deployment needs to exist so that in event of loss of the
> primary OpenStack site, the tenant can continue development. In addition to
> volume replication as in (1), subject to policies and SLAs, cold migration
> may be performed on a VM's volumes upon shutdown (or dismount) and tenant
> end-users can explicitly request replication of a volume that is in an
> application-consistent state (when they have quiesced it by VSS, dismount,
> or equivalent).
> >
> > a. Being down for a short period may be acceptable to this tenant. If
> all the hosts on the primary site are rebooted, for instance, due to power
> failure, it is the operators choice to fail over or not. If the operator
> chooses not to fail over, upon reboot of the VM's at the primary site, any
> established replication should automatically be continued.
> >
> >
> >
> > * (5) [Scale-out workload]
> >
> > A tenant has a Cassandra (or Hadoop or similar type of system)
> consisting of 75 VMs. Use is bursty. The system is used by a pharmaceutical
> company for design work. Loss of a week's work can be repeated, but weekly
> replication is mandatory. The application itself may provide some form of
> built-in geo-replication. Some controller-type VMs may need to be
> replicated as in (1). Other VMs may partner with replica VMs for explicit
> application data replication. For weekly replication of Cassandra data,
> Cassandra user-level snapshots are made into replicated volumes attached to
> each Cassandra VM. Replication is periodic with respect to the last
> replication event, that is, only data changed since the last replication
> event is sent.
> >
> >   a. The tenant requires use of a particular aggregated network link for
> replication.
> >
> >   b. The tenant requires custom integration with the DR replication
> workflow to quiesce Cassandra via user-level commands and scripts developed
> by the end-user.
> >
> >   c. Initial synchronization of replicated primary and secondary volume
> need not be over a network link. Secondary volumes can be created initially
> from physical disks or backups physically moved to the secondary site.
> >
> >
> >
> > * (6) [Degraded-mode Mission-critical single VM]
> >
> > This single VM use case is similar to (1), but when a network
> > partition occurs between the primary and secondary OpenStack sites,
> > with both sites remaining up, the primary VM remains operational while
> > the secondary replica VM also comes online. Both VMs operate in a mode
> > that resembles replication with a momentary network fault, logging
> > their would-be replication traffic for continuation when the network
> > comes back. When network connectivity is reestablished, one site again
> > becomes the primary and differences in the VM's volumes can optionally
> > (as controlled by policy) be reconciled. (In a simple case, each site
> > might have its own dedicated volume partition or attached volume with
> > its latest state.)
> >
> >
> >
> > * (7) [Self-contained application volume]
> >
> > A cinder volume contains a complete database application, including the
> database and all binaries and configuration files. Replication of the
> entire VM to which this volume is attached is not needed. The VM and  its
> configuration can be recreated on demand at the remote site and attached to
> the replicated application volume. The DR system still needs to orchestrate
> the process and create or manage the required network environment. A simple
> DR strategy can be used in which the volume is quiesced on the primary, a
> volume snapshot taken, the volume unquiesced (enabling the VM to continue
> running), and a backup is then made of the snapshot. Backups can be
> transported by whatever means to the DR site, where the volume can be
> restored to its state at time of snapshot.
> >
> >
> >
> > * (8) [Stateless]
> >
> > No volumes and VMs need to be replicated, as VMs and their configuration
> can be recreated on demand, using configuration tools, and application data
> is accessed over the wide-area network (NFS or object store). The DR
> process still has to orchestrate creating the VMs, running configuration
> tools to populate them, creating the network environment, and booting VMs
> in required order.
> >
> >
> >
> > * (9) [Site Evacuation]
> >
> > The holy grail, automatic planned migration of the workload and data
> from one cloud-scale datacenter to another (or a set of others). In
> practice, likely to include admins in-the-loop. At both tenant-scale and
> entire datacenter scale. The entire cloud datacenter is expected to go
> offline for an extended period (the hurricane scenario).
> >
> >
> >
> > -bruce
> >
> >
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
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