HTTP: Complete Guide — Headers, Status Codes, Protocols

Enterno.io Editorial Team

Glossary (75) all →

Rust web frameworks — Axum, Actix, Rocket

Rust web frameworks in 2026: Axum, Actix Web, Rocket, Warp. Comparison, latency, the Tokio async runtime.

WebAssembly Component Model

WebAssembly Component Model: WIT interfaces, portable binaries, language interop. Wasmtime, JCO, ComponentizeJS.

WebGPU — GPU API for the web

WebGPU: WebGL replacement, compute shaders, WGSL, access to Vulkan/Metal/D3D12. Chrome 113+, Firefox 141+.

Cloudflare R2 — S3-compatible storage

Cloudflare R2: zero egress fee, S3 API, rclone, hosted on 300+ locations. Compared with S3 / B2 / Wasabi.

WASI — WebAssembly System Interface

WASI: POSIX-like interface for WASM outside the browser. WASI 0.2, preview2, wasmtime, Fastly, Fermyon Spin.

Serverless Containers — Cloud Run, Fargate, Fly

Serverless containers: Cloud Run, ECS Fargate, Fly Machines. Container instead of function, scale-to-zero, no cold start.

React Server Components (RSC) — What It Is

React Server Components: server-only rendering, zero JS bundle to client. Next.js 13+, async components, streaming.

Streaming SSR — Progressive Rendering

Streaming SSR: server sends HTML in chunks as they become ready. Suspense, Transfer-Encoding: chunked, TTFB drops.

Edge Runtime — JS on Edge CDN

Edge Runtime: V8 Isolates, Cloudflare Workers, Vercel Edge, Deno Deploy. Low latency, no Node APIs.

Turbopack — Rust Bundler for Next.js

Turbopack — Webpack successor by Vercel. Rust, incremental, 10x faster. Stable in Next.js 15+.

Islands Architecture — Partial Hydration

Islands architecture: static HTML + interactive JS "islands". Astro, Fresh, Qwik. Minimal JS payload.

Partial Hydration — Selective JS Activation

Partial hydration: only interactive components get JS event handlers. React Server Components, Astro, Marko.

View Transitions API — Smooth Page Transitions

View Transitions API: DOM state changes with native animations without JS libraries. Chrome 111+, same-document + cross-document.

Web Streams API — ReadableStream

Web Streams API: chunked data processing in browser + Node.js. Fetch streaming, compression, crypto, SSE.

Shadow DOM — Web Components Encapsulation

Shadow DOM: scoped DOM tree + CSS for Web Components. Does not leak outer styles, used in React Native Web, Ionic.

Import Maps — JS without a Bundler

Import Maps: browser-native mapping of bare specifiers to URL. npm without webpack, dev without a bundler, CDN imports.

Data Lake vs Data Warehouse

Data Lake: raw data (Parquet, JSON) in object storage. Warehouse: structured + optimised for queries (Snowflake, BigQuery).

dbt — Data Build Tool

dbt: SQL-based transformation layer in the modern data stack. Ref(), tests, docs, lineage. Jinja templating.

Apache Iceberg — Lakehouse Table Format

Apache Iceberg: ACID table format for data lake. Netflix origin, Snowflake/BigQuery/Databricks support 2024+.

Apache Parquet — Columnar Storage Format

Apache Parquet: columnar format for data lake. Compression, column pruning, predicate pushdown. Used by Spark, Trino, DuckDB.

Apache Avro — Schema-first Data Format

Apache Avro: row-oriented data format for Kafka, streaming. Schema registry, backwards compatibility.

LLM (Large Language Model) — What It Is

LLM — large language model. GPT-5, Claude Opus 4.7, Gemini 2.5, Llama 3. Architecture, inference, sizes.

RAG (Retrieval-Augmented Generation)

RAG — LLM technique with vector DB search + context injection. LlamaIndex, LangChain, Pinecone/Qdrant.

Vector Embedding — What It Is

Vector embedding: numeric representation of text/image/audio in N-dim space. OpenAI, Cohere, jina, bge.

Vector Database — What It Is

Vector DB: optimised DB for ANN search on embeddings. Qdrant, Pinecone, Weaviate, Milvus, pgvector.

LLM Fine-tuning — Supervised + LoRA

Fine-tuning: continued training of an LLM on your own data. LoRA, QLoRA, full FT. OpenAI, Together, Hugging Face.

LLM Quantization — INT8/INT4

Quantisation: compressing LLM to low-bit weights. GGUF, GPTQ, AWQ. Running 70B on consumer GPU.

Semantic Search — Meaning-based Search

Semantic search: search via embeddings + ANN instead of keyword match. Hybrid search. Elasticsearch, Qdrant.

HNSW Index — ANN for Vectors

HNSW: Hierarchical Navigable Small World graph. Fastest ANN index for vector search. Parameters M, ef.

AI Agent — Autonomous LLM + Tools

AI Agent: LLM + memory + tools + planning. ReAct, AutoGPT, Claude Agent SDK, LangGraph.

Tool Calling (Function Calling) in LLM

Tool Calling: LLM invokes external functions via structured JSON. OpenAI, Anthropic, Gemini API.

MoE (Mixture of Experts) — Sparse LLM

MoE: sparse transformer with expert routing. Mixtral, DeepSeek, GPT-4 internals. 1.8T params but 400B active.

Transformer — LLM Architecture

Transformer: attention-based neural network. Self-attention, multi-head, positional encoding. Basis of GPT, BERT, LLaMA.

Context Window — What It Is in LLM

Context window: max tokens the model remembers. Claude 1M, Gemini 2M, GPT-5 1M. Long context vs RAG.

Service Mesh — What It Is, Istio, Linkerd

Service Mesh: infrastructure layer for service-to-service communication. Istio, Linkerd, Consul. mTLS, retries, observability.

Sidecar Pattern — Container Architecture

Sidecar pattern: auxiliary container alongside the main one. Logging, proxies, config reload. K8s multi-container pods.

Envoy — Proxy + Service Mesh Data Plane

Envoy: high-performance L7 proxy from Lyft. Backbone of Istio, AWS App Mesh. Configuration, filters.

Istio — Service Mesh for Kubernetes

Istio: most-featured service mesh. Envoy sidecars + istiod control plane. mTLS, traffic shaping, observability.

Kubernetes Operator — Custom Controllers

K8s Operator: custom controller + CRD for stateful apps. Postgres, Redis, Kafka operators. OperatorHub.

Helm — Kubernetes Package Manager

Helm: templating + packaging Kubernetes manifests. Charts, values.yaml, Helm Hub, OCI registries.

GitOps — Declarative Deploy via Git

GitOps: infrastructure + app state in Git, automated sync. Flux, ArgoCD. 4 principles.

ArgoCD — GitOps for Kubernetes

ArgoCD: declarative GitOps continuous delivery. App-of-apps pattern, sync, rollback. UI + CLI.

Terraform — Infrastructure as Code

Terraform: declarative IaC from HashiCorp. HCL, providers, state, modules. BSL license change 2023.

OCI Image — Open Container Initiative Format

OCI: open container image standard. Docker-compatible. Manifests, layers, registries.

CDC — Change Data Capture

Change Data Capture: stream DB changes in real-time. Debezium, Kafka Connect, WAL, binlog.

Materialized View — What It Is

Materialized view: precomputed query result stored as a table. Postgres, Oracle. Refresh strategies.

Event-Driven Architecture — EDA

Event-driven architecture: services communicate via events. Kafka, RabbitMQ, pub/sub. Loose coupling.

WASI — WebAssembly System Interface

WASI: POSIX-like API for WebAssembly outside the browser. Server-side WASM, Fastly, Fermyon, plugins.

CQRS — Command Query Responsibility Segregation

CQRS — separation of read and write models in architecture. When to use, with Event Sourcing, examples.

Event Sourcing — What It Is

Event Sourcing — architectural pattern: store events, not state. EventStore, Kafka, replay. Pros and cons.

Saga Pattern — Distributed Transactions

Saga pattern: long-running distributed transactions via events, compensation. Choreography vs orchestration.

Bloom Filter — Probabilistic Data Structure

Bloom filter — data structure for fast membership check with false positives. Redis, CDN, Cassandra.

Consistent Hashing — Distributed Sharding

Consistent hashing: distribute keys across nodes with minimal reshuffle on scaling. Ring, virtual nodes, rendezvous.

Canary Release — Gradual Rollout

Canary release — roll out a new version to % of traffic. Difference from blue-green, feature flags. Prometheus alerts.

Blue-Green Deployment

Blue-Green deployment: 2 identical envs, instant switch. Rollback in a second. DB migrations challenge.

Feature Flags — Runtime Toggles

Feature flags (toggles): turn features on/off without deploy. LaunchDarkly, GrowthBook, Unleash. A/B testing.

Observability — 3 Pillars

Observability: metrics, logs, traces. Difference from monitoring. OpenTelemetry standard.

OpenTelemetry — Observability Standard

OpenTelemetry (OTel): vendor-neutral standard for metrics, logs, traces. CNCF. Auto-instrumentation.

SRE — Site Reliability Engineering

SRE: Google-originated discipline. Toil, error budgets, SLO-driven. Differs from DevOps.

FinOps — Cloud Cost Management

FinOps: practice of optimising cloud spend. FinOps Foundation, principles, RI/Savings Plans.

Jaeger — Distributed Tracing

Jaeger — open-source distributed tracing (Uber, CNCF graduated). Spans, service map, architecture.

LRU Cache — Least Recently Used

LRU cache: eviction policy. Redis allkeys-lru, HashMap+DoubleLinkedList. O(1) implementation.

Log Aggregation — Centralising Logs

Log aggregation: collect logs into central store. ELK, Loki, Splunk, CloudWatch. Architecture, cost.

gRPC — What It Is, vs REST

gRPC is a high-performance RPC protocol from Google. Protobuf, HTTP/2, streaming. Difference from REST.

IndexedDB — Browser NoSQL Database

IndexedDB — browser-built-in NoSQL DB. Async, transactional, large storage. For PWA and offline-first.

WebSocket — Real-Time Bidirectional

WebSocket (RFC 6455) — a full-duplex connection over TCP. Real-time chat, notifications, games. Difference from HTTP.

SSE — Server-Sent Events

SSE (Server-Sent Events) — server-to-client streaming over HTTP. Simpler than WebSocket, works through any proxy.

Token Bucket — Rate Limiting Algorithm

Token bucket — rate limiting algorithm with burst. Difference from leaky bucket, sliding window, fixed window.

SLI / SLO / SLA — Differences

SLI (Service Level Indicator), SLO (Objective), SLA (Agreement) — foundations of reliability engineering. 99.9% examples.

GraphQL — What It Is

GraphQL — a query language for APIs. Single endpoint, client requests only the fields needed. Difference from REST.

CRDT — Conflict-Free Replicated Data Types

CRDT — data structures for real-time collaborative editing. Yjs, Automerge, offline-first without server-mediated merge.

Webhook — What It Is and How It Works in 2026

A webhook is an HTTP POST callback from a service to your URL on an event. Difference from polling, HMAC signing, best practices.

Edge Computing — What It Is and Why It Matters

Edge computing runs code on the nearest point (edge) to the user. Cloudflare Workers, AWS Lambda@Edge, Deno Deploy. Different from CDN.

Idempotency in APIs — What It Means

Idempotency — a property where an operation produces the same result on N executions. Idempotency-Key in POST, GET vs POST, patterns.

robots.txt — What It Is and How It Works

robots.txt is a file with instructions for search bots. User-agent, Disallow, Allow, Sitemap, Crawl-delay. Common mistakes and checks.

How-to (30) all →

How to Generate SBOM for Supply Chain

SBOM (Software Bill of Materials): syft, CycloneDX, SPDX. CISA compliance, executive order 14028, sign + attest with cosign.

How to Set Up OpenTelemetry — 2026

OpenTelemetry (OTel): standard for traces + metrics + logs. Setup Node/Python + collector + backend (Jaeger/Grafana/Datadog).

How to Trace Distributed HTTP/gRPC Calls

Distributed tracing via OpenTelemetry: traceparent headers, context propagation, span correlation. Jaeger, Tempo, Honeycomb.

How to Measure SLI/SLO for a Service

SLI + SLO + error budget: SRE practices. Latency p99, error rate, availability. Alert when budget exhausted.

How to Set Up Prometheus Alerting — Alertmanager

Prometheus Alertmanager: rules, routing, deduplication, PagerDuty/Slack/Email integration. Best alerting practices.

How to Set Up Structured Logging — JSON Logs

Structured logging: JSON format, correlation IDs, log levels, Pino/Winston/Zap. Elasticsearch/Loki/Datadog backends.

How to Build a RAG Chatbot on Docs — 2026

Step-by-step: embeddings → vector DB → retrieval → LLM. LangChain, Qdrant, OpenAI. Full example in 30 min.

How to Fine-tune LLM on Your Data — 2026

Fine-tune LLM via LoRA / OpenAI / Together.ai. Prepare JSONL dataset, train, eval, deploy.

How to Deploy a Vector Database — 2026

Qdrant, pgvector, Weaviate setup. Docker deploy, collection config, HNSW tuning, monitoring.

How to Stream LLM Responses in Real Time

Server-Sent Events, streaming LLM answers in browser. OpenAI, Claude, Gemini. Fetch API + ReadableStream.

How to Cache LLM API Calls — 2026

Redis cache for LLM responses. Exact match + semantic cache. Anthropic prompt cache. 10x cost reduction.

How to Evaluate LLM Output Quality — 2026

Ragas, LangSmith, LLM-as-judge. Automatic metrics for RAG, chatbot, code generation. CI/CD eval pipelines.

How to Build an AI Agent with MCP — 2026

Model Context Protocol (MCP) from Anthropic: expose tools to LLM. Claude Desktop, Zed IDE, custom servers.

How to Deploy LLM on Serverless GPU — 2026

Modal, RunPod, Replicate, Cloudflare Workers AI. Serverless GPU for LLama 3, Mistral, custom models.

How to Add Semantic Search to a Site — 2026

Embeddings-based search for blogs, docs, e-commerce. OpenAI + Qdrant + native UI.

How to Set Up CI/CD in GitHub Actions — 2026

Step-by-step CI/CD in GitHub Actions: workflow YAML, jobs, matrix, secrets, deploy to server. Full example.

How to Set Up GitOps with ArgoCD — 2026

Step-by-step GitOps with ArgoCD: install, first Application, auto-sync, multi-cluster, app of apps.

How to Find and Fix Slow Postgres Queries

PostgreSQL performance: pg_stat_statements, EXPLAIN ANALYZE, indexes, N+1 queries, connection pooling.

How to Migrate an Application to Kubernetes — 2026

Step-by-step migration from VPS/Docker Compose to Kubernetes: containerization, manifests, Helm, observability.

How to Set Up Redis Cluster — 2026

Redis Cluster setup: 6 nodes, sharding, replication. Automated failover, client-side routing. Production guide.

How to Use Docker Compose — 2026

Docker Compose: multi-container apps via docker-compose.yml. Networks, volumes, env files, scaling, healthchecks.

How to Debug nginx Errors — 2026

nginx error debugging: error.log, -t config test, debug module, 502/504 causes, permissions.

How to Set Up Cloudflare CDN for a Site — 2026

Cloudflare setup: DNS, Proxy (orange cloud), SSL/TLS, Page Rules, cache, security. Free tier setup.

How to Set Up an nginx Reverse Proxy — 2026

Step-by-step nginx reverse proxy setup. proxy_pass, headers, X-Real-IP, load balancing, WebSocket upgrade.

How to Set Up Prometheus + Grafana — 2026

Install Prometheus + Grafana: Docker compose, scrape config, data source, dashboards, Node exporter.

How to Set Up PostgreSQL Backups — 2026

Step-by-step PostgreSQL backup: pg_dump, pg_basebackup, WAL archiving, point-in-time recovery (PITR). S3 storage.

How to Create a systemd Service — 2026

Step-by-step systemd unit file for Node.js/Python/Go apps. Auto-start, restart policy, logs, security.

How to Configure logrotate — 2026

Step-by-step logrotate setup for application logs. Daily rotation, compression, retention, post-rotate hooks.

How to Set Up a CDN — Cloudflare, AWS, Yandex 2026

Step-by-step CDN setup: Cloudflare free, AWS CloudFront, Yandex Cloud CDN. DNS, SSL, cache rules.

How to Set Cache-Control Headers — 2026 Guide

Proper Cache-Control, ETag, Last-Modified setup for static assets and HTML. nginx and Apache examples, TTL per content-type.

Alternatives (43) all →

Grafana Alternatives 2026 — Observability Dashboards

Grafana — #1 OSS dashboards. Alternatives: Datadog, New Relic, Chronograf, Kibana, Prometheus Console. Self-host vs SaaS.

Honeycomb Alternatives 2026 — Distributed Tracing

Honeycomb — observability for high-cardinality queries. Alternatives: Datadog, Lightstep, Jaeger, Tempo, Chronosphere.

Grafana Loki Alternatives 2026 — Log Aggregation

Grafana Loki — cheap log storage (label-indexed). Alternatives: Elasticsearch, OpenSearch, ClickHouse, Quickwit, VictoriaLogs.

Snowflake Alternatives 2026 — Cloud Data Warehouse

Snowflake — market leader cloud warehouse. Alternatives: BigQuery (Google), Redshift (AWS), Databricks, ClickHouse Cloud, DuckDB.

ClickHouse Alternatives 2026 — Analytics DB

ClickHouse — open-source OLAP, Yandex origin. Alternatives: DuckDB, Apache Pinot, StarRocks, Druid, MonetDB.

Apache Airflow Alternatives 2026 — Data Orchestration

Apache Airflow — de-facto workflow orchestrator. Alternatives: Prefect, Dagster, Temporal, Mage, Kestra, Argo Workflows.

Fivetran Alternatives 2026 — Managed ETL/ELT

Fivetran — #1 managed ELT (350+ connectors). Alternatives: Airbyte (open source), Stitch, Hevo, Estuary, Rivery.

Segment Alternatives 2026 — CDP (Customer Data)

Twilio Segment — leading CDP. Alternatives: RudderStack (open), Snowplow, Jitsu, Avo, Freshpaint, PostHog.

Looker Alternatives 2026 — BI / Semantic Layer

Looker (Google) — BI with semantic layer. Alternatives: Metabase, Superset, Cube, Preset, Lightdash, Mode.

Vercel Alternatives 2026 — Next.js Hosting

Vercel — #1 Next.js deploy. Alternatives: Netlify, Cloudflare Pages, AWS Amplify, Render, Railway, self-host.

ChatGPT Alternatives 2026 — Claude, Gemini, DeepSeek

ChatGPT GPT-5 leads the market. Alternatives: Claude Opus 4.7, Gemini 2.5, DeepSeek R1, Llama 3, Mistral.

GitHub Copilot Alternatives 2026 — AI Coding Assistants

Copilot $10/mo. Alternatives: Cursor, Codeium (free), Continue, Cody, Tabnine, Claude Code, Zed AI.

Midjourney Alternatives 2026 — Image Generation

Midjourney $10-120/mo. Alternatives: Flux Pro, DALL-E 3, Ideogram, Recraft, Stable Diffusion XL, FLUX.1.

Perplexity AI Alternatives 2026 — AI Search

Perplexity $20/mo. Alternatives: You.com, Phind (dev-focused), Exa, Brave Search AI, ChatGPT Search.

Pinecone Alternatives 2026 — Managed Vector DB

Pinecone $70+/mo. Alternatives: Qdrant Cloud, Weaviate Cloud, Milvus Zilliz, Upstash Vector, pgvector.

LangChain Alternatives 2026 — LLM Frameworks

LangChain — most popular LLM framework. Alternatives: LlamaIndex, Haystack, DSPy, Semantic Kernel, Vercel AI SDK.

Cursor IDE Alternatives 2026 — AI Code Editors

Cursor $20/mo. Alternatives: VS Code + Copilot, Zed, Windsurf, Void, Aider (CLI), Continue (open source).

Notion AI Alternatives 2026 — AI in Knowledge Tools

Notion AI $10/user. Alternatives: Mem.ai, Obsidian + AI plugins, Reflect, Logseq, Capacities, Craft.

OpenAI API Alternatives 2026 — LLM Providers

OpenAI API is the default. Alternatives: Anthropic, Google Gemini, Together.ai, Groq, Fireworks, Replicate.

Hugging Face Alternatives 2026 — Model Hubs

Hugging Face — #1 ML model hub. Alternatives: Replicate, Modal, Together.ai, Kaggle Models, GitHub Hub.

DataGrip Alternatives 2026 — SQL IDE without subscription

DataGrip by JetBrains is $229/year. Alternatives: DBeaver, TablePlus, pgAdmin, Beekeeper Studio, native AI integrations.

TablePlus Alternatives 2026 — Fast SQL Client

TablePlus is $89 lifetime. Alternatives: DBeaver (free), Beekeeper Studio, Sequel Ace, DataGrip, Postico for macOS.

pgAdmin Alternatives 2026 — Postgres GUI

pgAdmin is default for Postgres but heavy UI. Alternatives: DBeaver, TablePlus, Postico, DataGrip, Beekeeper Studio.

DBeaver Alternatives 2026 — SQL IDE

DBeaver is the #1 open source SQL IDE. Alternatives: DataGrip, TablePlus, Beekeeper Studio, HeidiSQL, MySQL Workbench.

MinIO Alternatives 2026 — Self-hosted S3

MinIO is open source S3-compatible. Alternatives: SeaweedFS, Garage, Ceph Rados Gateway, Storj, Backblaze B2.

Backblaze B2 Alternatives 2026 — Cheap S3

Backblaze B2 is the cheapest S3-compatible cloud storage ($6/TB/mo). Alternatives: Wasabi, Storj, iDrive e2, Cloudflare R2.

Wasabi Alternatives 2026 — Cold Cloud Storage

Wasabi $6.99/TB with no egress fees. Alternatives: Backblaze B2, Cloudflare R2, iDrive e2, AWS S3 Glacier.

Storj Alternatives 2026 — Decentralized Storage

Storj — decentralized S3-compatible cloud. Alternatives: Sia, Filecoin, Arweave, IPFS + Filebase, Backblaze B2.

Lens Alternatives 2026 — Kubernetes IDE

Lens Desktop is a popular Kubernetes IDE. Alternatives: k9s (terminal), Headlamp (web), Octant, Rancher Desktop, OpenLens.

k9s Alternatives 2026 — Kubernetes Terminal UI

k9s is the #1 terminal UI for Kubernetes. Alternatives: kube-capacity, Lens / OpenLens, Headlamp, stern (logs), kubectx.

Postman Alternatives 2026 — API Testing Tools

Postman moved many features to paid in 2024. Alternatives: Enterno.io, Insomnia, Hoppscotch, Bruno, Thunder Client.

Insomnia Alternatives 2026 — API Clients

Insomnia (Kong) — open-source API client. Alternatives: Enterno.io, Postman, Hoppscotch, Bruno, Thunder Client.

Hoppscotch Alternatives 2026 — Web API Clients

Hoppscotch — open-source web-based API client. Alternatives: Enterno.io, Postman, Insomnia, Bruno.

LogRocket Alternatives 2026 — Session Replay

LogRocket — session replay + error tracking. Alternatives: Enterno.io RUM, Fullstory, Hotjar, Sentry Session Replay.

Hotjar Alternatives 2026 — Heatmaps, Polls

Hotjar — heatmaps + session recordings + surveys. Alternatives: Enterno.io RUM, Microsoft Clarity, Fullstory, Yandex Metrika.

Plausible Alternatives 2026 — Privacy Analytics

Plausible — lightweight privacy-focused analytics. Alternatives: Enterno.io RUM, Umami, Fathom, Simple Analytics.

Umami Alternatives 2026 — Self-Hosted Analytics

Umami — open-source privacy analytics. Alternatives: Enterno.io RUM, Plausible, Matomo, Simple Analytics, Yandex Metrika.

Datadog Alternatives 2026 — Observability

Datadog — enterprise APM + infrastructure monitoring. Alternatives: Enterno.io, New Relic, Grafana Cloud, self-hosted Prometheus.

New Relic Alternatives 2026 — APM

New Relic — APM + infrastructure monitoring. Alternatives: Enterno.io, Datadog, Grafana, Elastic APM.

Oh Dear Alternatives — Application Monitoring 2026

Oh Dear is full-stack site monitoring. Alternatives: Enterno.io, BetterUptime, Checkly, UptimeRobot.

Updown.io Alternatives 2026 — Simple Uptime Monitor

Updown.io is a minimalist uptime monitor with pay-as-you-go. Alternatives: Enterno.io, UptimeRobot, BetterUptime, StatusCake.

Downdetector Alternatives 2026 — Outage Tracking

Downdetector aggregates outage reports. Alternatives: Enterno.io status, Istheservicedown, OutageReport, Status Gator.

Host-Tracker Alternatives 2026 — Russian Monitors

Host-Tracker is a Ukrainian monitoring service since 2010. Alternatives for RU: Enterno.io, UptimeRobot, Yandex Cloud Monitoring.