Mirroring 101

Caché mirroring is a reliable, inexpensive, and easy to implement high availability and disaster recovery solution for Caché and Ensemble-based applications. Mirroring provides automatic failover under a broad range of planned and unplanned outage scenarios, with application recovery time typically limited to seconds. Logical data replication eliminates storage as a single point of failure and a source of data corruption. Upgrades can be executed with little or no downtime.

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In this post I show strategies for backing up Caché using External Backup with examples of integrating with snapshot based solutions. The majority of solutions I see today are deployed on Linux on VMware so a lot of the post shows how solutions integrate VMware snapshot technology as examples.

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ISCAgent is automatically installed with Cache, runs as a service and can be configured to
start with the system. This is fine – but the complication comes when this is on VCS clusters with
Mirroring on. When installing a Single Instance of Cache in a Cluster, point number 2. Says “Create
a link from /usr/local/etc/cachesys to the shared disk. This forces the Caché registry and all
supporting files to be stored on the shared disk resource you have configured as part of the
service group.”

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Question
William Proctor · Mar 23, 2017
problem with Mirroring

Hello,  Thanks in advance for all replies.  I have been practicing setting up mirroring between two development servers in preparation for mirroring our production server in a few weeks.  I started by setting the servers up with minimum security which worked easily, then I set it up in lock down mode again without any issues.  Now I am setting it up in lockdown mode with encryption and this one is testing me.  I have everything setup but my async dr member cannot connect to the primary.

 

from cconsole.log

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++ Update: August 1, 2018

The use of the InterSystems Virtual IP (VIP) address built-in to Caché database mirroring has certain limitations. In particular, it can only be used when mirror members reside the same network subnet. When multiple data centers are used, network subnets are not often “stretched” beyond the physical data center due to added network complexity (more detailed discussion here). For similar reasons, Virtual IP is often not usable when the database is hosted in the cloud.

Network traffic management appliances such as load balancers (physical or virtual) can be used to achieve the same level of transparency, presenting a single address to the client applications or devices. The network traffic manager automatically redirects clients to the current mirror primary’s real IP address. The automation is intended to meet the needs of both HA failover and DR promotion following a disaster. 

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Question
Joan Cruz · Aug 2, 2016
Use of $ZUTIL(49) is deprecated

Hi all,

I'm using $ZUTIL(49) to get information of the databases I want to add to a mirror. This information is passed to ##class(SYS.Mirror).CatchupDB(plstPathDatabases)  in order to Catchup all databases addes to a Mirror.

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I've created a scheduled task that dumps HL7 messages to flat files. It uses the OutputToLibraryStream() method of EnsLib.HL7.Message. I'd like to be able to run it on a mirror member host whether it's primary or backup.

When run against a database that's mounted read-only, it works fine. However, when I attempt to run it against a mirror backup database, I get the following error:

#5002: Cache error: <PROTECT>%LoadData+7^EnsLib.HL7.Message.1

Tracing that back to the source, I find:

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Hi, would really appreciate your advice on how I can restart the mirror-monitor. I've followed the instructions and restarted the mirror monitor, and still the status seems to be down. Can you point me to some resource or steps that I can follow ?

I logged into %SYS terminal and restarted the mirror monitor and it says that it is running

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In this article, we’ll build a highly available IRIS configuration using Kubernetes Deployments with distributed persistent storage instead of the “traditional” IRIS mirror pair. This deployment would be able to tolerate infrastructure-related failures, such as node, storage and Availability Zone failures. The described approach greatly reduces the complexity of the deployment at the expense of slightly extended RTO.

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Question
Mikhail Khomenko · Oct 30, 2016
ISCAgent debug

Good day!
Is there an opportunity to debug the ISCAgent behaviour (in Linux)? ISCAgent uses /etc/iscagent/iscagent.conf as configuration file, but in docs I've found a description only for two parameters (port number and interface - http://docs.intersystems.com/latest/csp/docbook/DocBook.UI.Page.cls?KEY=...). Other parameters I can see by running /usr/local/etc/cachesys/ISCAgentCtrl status:

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Hi,

Can a Cache Mirror be  used in the cloud ? (ie stand up a Primary and Backup member instances in a High Availability Cache Mirroring configuration) 

I'm investigating the validity of this configuration, because I was of the understanding that this may not possible due to these cloud servers not (typically) having fixed ip addresses, which interferes with the Virtual IP settings for the mirror set.

Is this correct, and if there are workarounds (like Load Balancing ?) can I have details on how this should be configured ?

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Question
Rich Taylor · Aug 18, 2016
Read only Async mirror setup

I have setup an async reporting mirror member with Read only access.  My problem is that if I try to do any sql reporting against that data I am getting errors.  I am sure that this is because the DB is read only, but I had assumed that setting up a reporting mirror would handle this.

 

I there a setting or mapping  I am missing?

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In this post, I am going to detail how to set up a mirror using SSL, including generating the certificates and keys via the Public Key Infrastructure built in to Caché. The goal of this is to take you from new installations to a working mirror with SSL, including a primary, backup, and DR async member, along with a mirrored database. I will not go into security recommendations or restricting access to the files. This is meant to just simply get a mirror up and running.

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When I create a TASK on the Primary mirror member and Try to create the same TASK in the backup mirror member,  It Gives me CSP Application error.

The TASK gets created in the Primary node without any errors and When creating in the Backup node it prompts the error.

It happens is IRIS and I didn't face this in CACHE.

Finally what I did is export the TASK in Primary and Imported in Backup.

Is this a feature of IRIS?

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Hello,

I work on deploying IRIS inside Docker container. I really like %Installer class can automate many steps. I want to establish an ECP connection to a mirror database and then define a remote database on the application server. I have already seen we can create local database and namespace in %Installer. What code is needed to establish ECP connection?

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Hello!

First of all, let me state that I am no senior InterSystems expert. 

In my organization, we have a HealthShare Health Connect setup where each namespace has one code database and one data database, which are both actively mirrored. We have two nodes in the mirror.

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Hey Developers,

We're pleased to invite you to join the next InterSystems IRIS 2020.1 Tech Talk: DevOps on June 2nd  at 10:00 AM EDT! 

In this InterSystems IRIS 2020.1 Tech Talk, we focus on DevOps. We'll talk about InterSystems System Alerting and Monitoring, which offers unified cluster monitoring in a single pane for all your InterSystems IRIS instances. It is built on Prometheus and Grafana, two of the most respected open source offerings available.

Next, we'll dive into the InterSystems Kubernetes Operator, a special controller for Kubernetes that streamlines InterSystems IRIS deployments and management. It's the easiest way to deploy an InterSystems IRIS cluster on-prem or in the Cloud, and we'll show how you can configure mirroring, ECP, sharding and compute nodes, and automate it all.

Finally, we'll discuss how to speed test InterSystems IRIS using the open source Ingestion Speed Test. This tool is available on InterSystems Open Exchange for your own testing and benchmarking. 

   

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++Update: August 2, 2018

This article provides a reference architecture as a sample for providing robust performing and highly available applications based on InterSystems Technologies that are applicable to Caché, Ensemble, HealthShare, TrakCare, and associated embedded technologies such as DeepSee, iKnow, Zen and Zen Mojo.

Azure has two different deployment models for creating and working with resources: Azure Classic and Azure Resource Manager. The information detailed in this article is based on the Azure Resource Manager model (ARM).

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Is it possible to make the cache terminal available over a mirrored vip address for a healthshare mirrored environment? So that connecting to a terminal for a mirrored environment will always connect to the Live Node?

 

I'm looking to write a Powershell script to run against the system and need to connect to the Live Node in a mirrored setup. Is this possible or am I going to have to log onto each node to establish which is Live.  Or does this even matter?

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Question
Mark Turner · Mar 15, 2019
How to shrink a WIJ

I have a DR Mirror   with a WIJ that is 5 times as large as the Primary Failover member. My Read-Write Reporting mirror WIJs are the same size as the Primary.  I don't  know why the DR WIJ i so large and would like to shrink it to the same size as the others.  Any suggestions are welcome. Thanks!

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In the context of IKO (Iris Kubernetes Operator) the question of Service not redirecting dynamically to the correct Pod is still pending.
In production this can be dangerous since an overload (or any other simpler problem) can cause you to change the main Pod and leave the application inoperable until we intervene.

Intersystems support warned that this is still an issue of IKO, but there are some possibilities that I am studying.

To explore an idea I had, I would like the help of this Forum to answer the following question:

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Question
Joan Cruz · May 7, 2018
Information of Mirror servers

Hi

I'm using this query "Config.MapMirror.List" To get information of the list of servers that are in the mirror system.

I'd like to know how can I know which of the list is the primary and which is the failover or async member.

Is there a way to do it with this query? Is there another query to get this info?

Thanks a lot

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In System Administration | Configuration |  System Configuration | Journal Settings there is a check box for Freeze on error.

From reading the documentation, it sounds like the choice to freeze on error is one of system availability vs system integrity.

Curious to know whether Ensemble users choose to freeze on error or not.

If you have a best practice recommendation based upon your experience or knowledge, that would be helpful information too.

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Hi All!

I asked previously about the DR server in the cloud but actually, I'm curious about the backup server to use as analytics server more than for recovery in DR case.

There is a recommended practice to use an async mirror as a server for BI (InterSystems Analytics, DeepSee)

The question is if I have PRIMARY in the cloud (AWS, Google, Azure, etc) "how far" should async mirror member be placed? Same cloud, same private cloud or it doesn't matter at all for analytics purposes?

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