Slack

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• Slack · Jul 14, 2026

  Shipyard: How We Built Slack’s Next-Generation EC2 Platform

  Slack developed Shipyard to modernize its EC2 infrastructure by replacing continuously updated, mutable instances with immutable deployable artifacts. The platform adopts a layered image architecture starting with a standardized base image called slack-zero, which is built using AWS Image Builder and consumed by downstream service-specific machine images. Rather than running periodic Chef jobs in the background, configuration management is restricted to image baking and initial instance provisioning phases. Fleet management is handled through the Peekaboo inventory system, metric-driven progressive rollouts via Gondola, and automated instance rotation managed by a lifecycle component known as the Reaper. Developers validate cookbook updates prior to merging using Ship Quick, which provisions real infrastructure across dedicated worker fleets to verify provisioning workflows.

  Archie Gunasekara

• Slack · Jun 11, 2026

  Agentic Testing: Where Agents Fit in the E2E Testing Stack

  Traditional end-to-end tests validate rigid user journeys, whereas agentic tests verify whether broad goals can be achieved by adapting actions dynamically. To evaluate agentic testing tradeoffs, researchers executed over 200 runs across Playwright Model Context Protocol (MCP), Playwright CLI, and agent-generated Playwright tests using Claude models. Playwright MCP demonstrated high reliability with failure rates of 0% on simple thread replies and approximately 12% on complex search discovery flows. Playwright CLI and generated code struggled more on complex workflows, exhibiting failure rates of approximately 20% and 48% respectively. Although generated tests were faster with average runtimes of roughly three minutes, agentic testing provides a distinct exploratory layer atop deterministic CI test suites.

  Sergii Gorbachov

• Slack · May 28, 2026

  Slack AI: The Path to Multi-Cloud

  Slack evolved its Slack AI serving infrastructure across multiple phases to handle enterprise LLM workloads reliably and securely. The initial deployment on AWS SageMaker provided zero-knowledge escrow VPC isolation and FedRAMP compliance, but engineers faced scaling latency, GPU scarcity, and significant operational overhead. Slack then migrated live traffic to Amazon Bedrock to leverage managed Model Units and eliminate model release lag without customer-facing incidents. However, fixed Provisioned Throughput commitments and regional peak traffic variations created persistent underutilization challenges. Consequently, Slack expanded into a multi-cloud orchestration architecture that normalizes disparate provider APIs, integrates unified cross-cloud telemetry, and routes traffic dynamically around latency spikes and outages.

  Shaurya Kethireddy

• Slack · May 5, 2026

  From SSH to REST: A Security-Driven Modernization of Slack’s EMR Data Pipelines

  Slack's data platform accumulated over 700 SSH-based Airflow operators executing jobs directly on AWS Elastic MapReduce clusters, creating broad security surfaces and operational instability. Stateful SSH connections frequently failed when Kubernetes pods restarted, leaving orphaned zombie processes and preventing infrastructure modernization such as migrating EMR clusters to child accounts. To eliminate SSH access, Slack adopted a REST-based architecture using Quarry, a gateway providing unified REST APIs and token authentication across compute engines. For non-Hadoop CLI workloads, Slack leveraged YARN Distributed Shell to execute arbitrary shell scripts stored in Amazon S3 within managed, isolated YARN containers. The phased migration achieved zero downtime across eight data regions, unlocking reliable monitoring, simplified onboarding, and future initiatives like Spark on Kubernetes.

  Mahendran Vasagam

• Slack · Apr 13, 2026

  Managing context in long-run agentic applications

  Long-running multi-agent systems struggle with context management because accumulating raw message histories degrades inference quality, increases latency, and exceeds context window limits. In a collaborative security investigation platform, passing unrestricted history can also introduce confirmation bias across specialized agents. To maintain coherence across unbounded rounds of investigation, the system eliminates raw message history carryover between invocations. Instead, it coordinates agents through three structured context channels: a Director's Journal for orchestration memory, a Critic's Review that scores findings to filter hallucinations, and a Critic's Timeline of validated chronological events. This architecture provides agents with tailored context without overwhelming their inference capacity.

  Dominic Marks

• Slack · Mar 31, 2026

  From Custom to Open: Scalable Network Probing and HTTP/3 Readiness with Prometheus

  Slack encountered a lack of client-side observability when introducing HTTP/3 at its edge. Because HTTP/3 runs over QUIC on UDP instead of TCP, neither existing commercial SaaS tools nor the internal Prometheus Blackbox Exporter could probe the new endpoints. To address this gap, an engineering intern integrated the open-source quic-go library into Prometheus Blackbox Exporter to build a native, configurable HTTP/3 probe. Slack deployed an internal implementation using the upstream functionality while waiting for pull request reviews, ultimately landing the contribution upstream. The resulting setup provides a unified view of HTTP/1.1, HTTP/2, and HTTP/3 metrics within Grafana, enabling reliable alerting and faster correlation with other telemetry.

  Carlo Preciado

• Slack · Mar 19, 2026

  How Slack Rebuilt Notifications 📣

  Slack redesigned its legacy notification architecture to address user confusion, conflicting desktop and mobile preference systems, and tight coupling between notification content and push delivery. The engineering team unified four separate preference models into a single framework with three channel options: All new posts, Mentions, and Mute. To ensure safe rollback and backwards compatibility without direct database mutations, Slack implemented a read-time translation strategy alongside a new desktop_push_enabled preference and auto-saving cross-platform React UI components. This decoupling of activity from push delivery resulted in a fivefold sustained increase in settings engagement, reduced reliance on per-channel overrides, and eliminated synchronization mismatches across mobile and desktop clients.

  Frances Coronel

• Slack · Dec 1, 2025

  Streamlining Security Investigations with Agents

  Slack's Security Engineering team handles billions of daily security events and needed a reliable way to streamline on-call alert triage. An initial prototype relying on a single 300-word prompt produced inconsistent results and frequently reached spurious conclusions without properly challenging assumptions. To gain precise control, the team decomposed the workflow into chained model invocations with structured JSON outputs organized across three agent personas: a Director, four domain experts, and a Critic. Domain experts gather raw evidence through tool calls, the Critic evaluates finding quality and synthesizes a timeline, and the Director steers investigation phases using tiered model costs. The multi-agent system enables engineers to supervise investigations via a real-time dashboard while uncovering emergent issues like credential exposures across process ancestry chains.

  Dominic Marks