Disaster Recovery Plan: How to Properly Brew Tea When the Server Room is Ablaze
It's high time to open the red envelope
In the life of any project, disaster is inevitable. We can't predict exactly what it will be — a short circuit in the server room, an engineer dropping the central database, or a beaver invasion. But rest assured, it will happen, and for the most absurd reason imaginable.
About the beavers, by the way, I wasn't kidding. In Canada, they chewed through a cable and left the entire Tumbler Ridge area without fiber optic communication. It seems like animals are on a mission to suddenly cut off your access to resources:
About the beavers, by the way, I wasn't kidding. In Canada, they chewed through a cable and left the entire Tumbler Ridge area without fiber optic communication. It seems like animals are on a mission to suddenly cut off your access to resources:
- Macaques chewing on wires
- Cicadas mistaking cables for branches, and digging them out to lay eggs inside.
- Sharks biting into Google's transatlantic cables
- And for a major telecom company, Level 3 Communications, squirrels were actually at the top of their problem list.
When to Start Writing Your DRP
Every hour an employee spends is money out of the pocket. An hour from an expert, who knows every makeshift fix and understands what could break, costs even more. Plus, often the expert and someone who can write in plain language are not the same person. Bottom line, a good document isn't cheap, and you need to know exactly when it's worth the investment.
You definitely need to get on it if:
Cluster of Hashicorp Vault became unresponsive because of a connectivity breach between data centers? Your billing system will feel uncomfortable without passwords. Here, you definitely need a DRP, which you could align with an architecture refactor.
You definitely need to get on it if:
- You have a clear failure point, but no straightforward instructions for its recovery.
- A server, node group, or database crash could bring your business to a halt and start a fast-spinning loss counter.
Cluster of Hashicorp Vault became unresponsive because of a connectivity breach between data centers? Your billing system will feel uncomfortable without passwords. Here, you definitely need a DRP, which you could align with an architecture refactor.
Write Documentation
Rarely do people enjoy writing documentation. I, for one, actually like it because it helps me shift away from routine tasks and focus on the architecture's transparency. Nonetheless, it's a critically important story since a few dozen minutes spent on a note could later save you thousands of dollars in a serious crash.
Straight off the bat, I want to highlight an important point: troubleshooting documentation is crucial, but it's not yet a DRP. We stick to the following approach:
Straight off the bat, I want to highlight an important point: troubleshooting documentation is crucial, but it's not yet a DRP. We stick to the following approach:
- The employee who understands the system best writes the information system passport. It includes the basic description, why this thing is even needed, which systems are connected to it, and who to run to if something breaks.
- An on-call finds a problem in the logs, or detects an outage. If fixing the issue requires some non-obvious actions, they document every detail, down to the list of console commands, and add it to the Troubleshooting section.
- If the outage recurs - we create a ticket to eliminate its cause.
- If it's impossible to fix the cause due to architectural or financial reasons, we attach to the alert description a link to internal documentation describing how to fix it.
Turning On Our Inner Paranoid
In general, we've got documentation, we understand how to fix the main problems, but we still don't have a DRP. For a real Disaster Recovery Plan, we first need to decide on a threat model.
There's a relatively limited list of what can break, usually boiling down to a small number of categories like this:
As a result of such work, our backlog usually grows sharply due to tasks like "If script N runs before script M, it will irreversibly destroy the central DB. We should fix that." What remains after clearing the technical debt is your threat model, including those very recidivist beavers, the cleaner in the server room, and other natural disasters beyond your control.
There's a relatively limited list of what can break, usually boiling down to a small number of categories like this:
- Application failure
- OS services failure
- Network failure
- Hardware failure
- Virtualization failure
- Orchestration system failure
As a result of such work, our backlog usually grows sharply due to tasks like "If script N runs before script M, it will irreversibly destroy the central DB. We should fix that." What remains after clearing the technical debt is your threat model, including those very recidivist beavers, the cleaner in the server room, and other natural disasters beyond your control.
Accept the Inevitable and Go Make Tea
So, you've come to the realization that everything will eventually break down. You've considered all possible factors, including your radio relay line being blocked by a festival of flying balloons and a new fire at one of your providers.
Now, it's time to write the DRP itself. No, it's not that extensive troubleshooting section you wrote earlier. The DRP, in essence, is like a red envelope containing instructions such as:
Therefore, our documents almost always start the same way:
"A brief high-level guide for the default scenario. What follows will be a lot of text and detailed variants. Let's start with the basic sequence:
Now, it's time to write the DRP itself. No, it's not that extensive troubleshooting section you wrote earlier. The DRP, in essence, is like a red envelope containing instructions such as:
- Pick up the blue phone receiver.
- Dictate to the operator: "Wish - Rusty - Seventeen - Dawn - Furnace - Nine - Kind-hearted - Homecoming - One - Cargo Car."
- Wait for the reply tone.
Therefore, our documents almost always start the same way:
"A brief high-level guide for the default scenario. What follows will be a lot of text and detailed variants. Let's start with the basic sequence:
- Brew some tea and stop panicking.
- Notify the responsible parties."
DRP Structure
Here's the approximate structure we use as a template. Of course, you can adapt it as needed.
| DRP | |
|---|---|
| Information System | Enigma cluster |
| Creation Date | 07.06.2022 |
| Last Update Date | 13.02.2024 |
| Update and Testing Frequency | 1 year |
| DRP Testing Date | 13.02.2024 |
- System Architecture
- Information Systems
- Notification of Responsible Parties
- Key Questions Before DRP
- What should I do by default?
- A brief high-level guide for the default scenario.
- When is this DRP applicable?
- Principles for choosing a deployment site.
- How to understand where the deployment will go?
- Decision Making and Situation Analysis
- The Order of Service Deployment and Timing
- RPO and RTO
- Instructions for Deploying DRP Infrastructure
- Additional Materials
- Who needs to be notified immediately about the start of an emergency?
- How to properly conduct an initial diagnosis before touching anything? Ready simple console commands, links to dashboards, and other useful things.
- How much time do I have? Can I try to fix the system, or do I need to start everything from scratch?
- How to understand that the emergency has ended, and we’ve returned to normal operation?
A good practice is to add an "Additional Materials" section at the end of the document. It can be referenced as needed from the main brief instruction and other documents. The Troubleshooting we described earlier fits well into this block. Any other additional information should also be moved to the end, to not disrupt the minimalist style of the main instruction. Gantt Charts Help Greatly in Complex Systems
If the service is complex and individual elements are deployed in parallel, I strongly recommend adding a Gantt chart, which visually describes the order of recovery and approximate timelines for each stage. Such information is harder to grasp in text form.
At the very end of your document, there should be a clear description of the conditions for canceling the emergency mode, so it’s clear when to switch the load back and return to normal operations.
The Importance of IaC
Overall, the concept of Infrastructure-as-Code (IaC) isn’t formally required for implementing a Disaster Recovery Plan (DRP). However, in most large information systems, engineers won’t meet the recovery timelines if they have to run from server to server, making emergency fixes in the configuration and changing DNS records on the fly.
It’s much more effective to describe all the primary and backup infrastructure in Terraform, and its configuration in Ansible. Optionally, you can even bake ready-made images with Hashicorp Packer if you adhere to the concept of immutable infrastructure.
In this case, you can achieve near-zero costs for keeping the DRP in a ready state. Structurally, it would look something like this:
It’s much more effective to describe all the primary and backup infrastructure in Terraform, and its configuration in Ansible. Optionally, you can even bake ready-made images with Hashicorp Packer if you adhere to the concept of immutable infrastructure.
In this case, you can achieve near-zero costs for keeping the DRP in a ready state. Structurally, it would look something like this:
- Describe your test and production infrastructure in Terraform.
- Describe your DRP infrastructure in Terraform, but add variables for deployment activation.
variable "enable_mysql_drp" {
description = "Condition for creation of DRP MySQL droplet. Droplet is created only if variable is true"
type = bool
default = false
}In main.tf, describe the necessary parameters for your temporary infrastructure and tie them to conditions:
resource "digitalocean_droplet" "rover3-mysql-central-nl-1" {
image = var.ol7_base_image
count = var.enable_mysql_drp ? 1 : 0
name = "mysql-central-nl-1.example.com"
region = var.region
size = "c2-32vcpu-64gb"
tags = ["enigma", "enigma-central", "enigma-mysql-central"]
monitoring = true
}Now, an engineer can deploy the entire temporary infrastructure with a few commands like these from your instructions:
cd ~/enigma/terraform/DO
terraform apply \
-var='enable_mysql_drp=true' \
-var='enable_indexator_drp=true' \
-var='enable_clickhouse_drp=true' \
-var='enable_statistics_drp=true'If you chose to use images already baked with Packer as the source for deploying emergency infrastructure, you’d get almost ready infrastructure within minutes. The overhead costs for storing the images are usually small, but they require constant updating.
Another option is the direct use of Ansible, which will configure the new infrastructure according to your configuration requirements. Don’t forget about the time for loading and restoring the database from a cold backup. It can be costly and time-consuming, so consider this in your planning.
Another option is the direct use of Ansible, which will configure the new infrastructure according to your configuration requirements. Don’t forget about the time for loading and restoring the database from a cold backup. It can be costly and time-consuming, so consider this in your planning.
A Brief Checklist
Here are a few key points to consider:
A neural network can quickly analyze raw logs and build hypotheses about the causes of a disaster. This is invaluable in cases where the on-call engineer doesn't know all the nuances of the fallen system. I'll talk more about this next time.
And if you need to go through your infrastructure with a fine-tooth comb, write a DRP, and help with testing, come to us at WiseOps. We'll help.
- Murphy's laws haven't been repealed. If something can fall, it will eventually fall, with a crash and side effects in unexpected places.
- Before starting, conduct a full analysis and show the business how much a potential disaster might cost, and how much the backup scenario for the DRP would be. Often after this, resources are allocated. Sometimes, they realize it would be cheaper if everything went down for a day than to have a full reserve on standby.
- Make sure your backups are being performed.
- Ensure that backups are not only performed but also can be restored.
- Engage your creative paranoia and describe the threat model.
- Write the DRP. Then take it and throw out most of the text so that the meaning isn’t lost. Add all excess to the end of the document. If needed, an engineer will look there.
- Include in the document phone numbers, Telegram accounts, and other contacts of all key people.
- DRP needs to be tested. Seriously, it's a must. Businesses never have time for these tasks, but it's a very important process. The infrastructure of any live project can change beyond recognition in a year, tokens can expire, accesses can disappear, and configurations can become invalid. Therefore, include at least an annual limited simulation in your business processes. Otherwise, in the event of a disaster, an engineer will enter commands from an outdated instruction and finish off your infrastructure.
- Give the DRP to interns in a limited environment and watch as they struggle with the document (evil laugh). Your plan is good if even the most inexperienced team member can figure it out.
A neural network can quickly analyze raw logs and build hypotheses about the causes of a disaster. This is invaluable in cases where the on-call engineer doesn't know all the nuances of the fallen system. I'll talk more about this next time.
And if you need to go through your infrastructure with a fine-tooth comb, write a DRP, and help with testing, come to us at WiseOps. We'll help.
Gumeniuk Ivan
DevOps Engineer