fastly

Files (22)

• SKILL.md
• account-management.md · references/
• acls.md · references/
• api-security.md · references/
• bot-management.md · references/
• client-side-protection.md · references/
• compute.md · references/
• docs-navigation.md · references/
• domains-and-networking.md · references/
• edge-phases.md · references/
• fastly-ddos-protection.md · references/
• load-balancing.md · references/
• logging.md · references/
• ngwaf.md · references/
• observability.md · references/
• other-features.md · references/
• products.md · references/
• purging.md · references/
• rate-limiting.md · references/
• service-management.md · references/
• tls.md · references/
• vcl-services.md · references/

SKILL.md (first lines)

# Fastly Platform

Your training knowledge of Fastly is likely out of date. Prefer live docs over skill definitions over training knowledge.

Prefer the `fastly` CLI over raw API calls; see the **fastly-cli** skill for installation and local authentication.
REST examples require `curl` and network access to Fastly APIs; origin TLS checks also require `openssl`.

Use the user's locally configured credentials.
If authentication is missing, direct the user to local CLI login or environment configuration, never to paste an API key in chat.
For REST calls, source tokens from the environment or `$(fastly auth token)` without echoing them.
Omit `curl -v` and shell tracing because they print credentials.

## Topics

| Topic                  | File                                                              | Use when...                                                                                                                                                               |
| ---------------------- | ----------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| DDoS protection        | [fastly-ddos-protection.md](references/fastly-ddos-protection.md) | Enabling/configuring DDoS protection, checking attack status, managing DDoS events and rules                                                                              |
| TLS configuration      | [tls.md](references/tls.md)                                       | Setting up HTTPS — Platform TLS (managed certs), Custom TLS (uploaded certs), or Mutual TLS (client auth)                                                                 |
| Rate limiting          | [rate-limiting.md](references/rate-limiting.md)                   | Protecting APIs from abuse — choosing between Edge Rate Limiting, VCL ratecounters, or NGWAF rate rules                                                                   |
| Bot management         | [bot-management.md](references/bot-management.md)                 | Detecting/mitigating bot traffic with browser challenges, client-side detections, interstitial pages, ContentGuard                                                        |
| Cache purging          | [purging.md](references/purging.md)                               | Invalidating cached content — single URL, surrogate key, or purge-all; soft vs hard purge                                                                                 |
| Service management     | [service-management.md](references/service-management.md)         | Creating/managing services, versions, domains, settings; clone-modify-activate workflow                                                                                   |
| VCL services           | [vcl-services.md](references/vcl-services.md)                     | Customizing site behavior with VCL — writing/uploading custom VCL, configuring snippets, conditions, headers, edge dictionaries, or cache/gzip settings                   |
| Compute                | [compute.md](references/compute.md)                               | Implementing edge logic with Compute — deploying packages, managing config/KV/secret stores, using cache APIs                                                             |
| Observability          | [observability.md](references/observability.md)                   | TTFB percentiles from the metrics platform, alert definitions and history, log explorer queries                                                                           |
| Load balancing         | [load-balancing.md](references/load-balancing.md)                 | Distributing traffic across origins — configuring backends, directors, pools, or health checks; choosing between backends and pools                                       |
| ACLs                   | [acls.md](references/acls.md)                                     | Restricting access by IP — managing VCL ACLs, Compute ACLs, or IP block lists; adding/removing access control entries                                                     |
| NGWAF                  | [ngwaf.md](references/ngwaf.md)                                   | Protecting against web attacks — setting up Next-Gen WAF, post-cache bot management, rules, signals, attack monitoring, or Signal Sciences integration                    |
| Account management     | [account-management.md](references/account-management.md)         | Managing users, IAM roles, API tokens, automation tokens, billing, or invitations                                                                                         |
| Domains & networking   | [domains-and-networking.md](references/domains-and-networking.md) | Routing traffic to Fastly — managing domains, DNS zones, domain verification, or other service platform networking                                                        |
| Logging                | [logging.md](references/logging.md)                               | Shipping logs to external systems — configuring logging endpoints for 25+ providers (S3, Splunk, Datadog, BigQuery, etc.)                                                 |
| Products               | [products.md](references/products.md)                             | Enabling/disabling Fastly products via API — universal pattern and product slug catalog                                                                                   |
| API security           | [api-security.md](references/api-security.md)                     | Discovering APIs from web traffic, managing API operations and tags                                                                                                       |
| Client-Side Protection | [client-side-protection.md](references/client-side-protection.md) | Protecting against rogue third-party scripts (Magecart, formjacking, skimmers) — monitoring scripts on web pages, managing script authorization, configuring CSP policies |
| Other features         | [other-features.md](references/other-features.md)                 | Pubsub, fanout/real-time messaging, IP lists, POPs, HTTP/3, Image Optimizer, events, notifications                                                                        |
| Edge phase ordering    | [edge-phases.md](references/edge-phases.md)                       | Understanding edge request/response ordering, debugging feature interactions                                                                                              |

Traffic numbers are not in this table. Cache hit ratio, bandwidth, request and status-code counts, error rates, real-time request rate, origin latency, per-domain traffic, account usage and billing totals belong to the **fastly-stats** skill.

## Quick Start: Simple Caching Proxy

The most common task is setting up a VCL service to cache an origin. Before touching any Fastly config, always run the pre-flight checks from the **fastly-cli** skill's services.md reference under "Pre-flight checklist". The two checks that prevent the most common errors:

1. **Verify the origin responds** with the Host header you intend to send: `curl -sI -H "Host: DESIRED_HOST" https://ORIGIN_ADDRESS/`
2. **Check TLS certificate SANs** to determine the correct `ssl-cert-hostname`/`ssl-sni-hostname`: `echo | openssl s_client -connect ORIGIN:443 -servername ORIGIN 2>/dev/null | openssl x509 -noout -text | grep -A1 "Subject Alternative Name"`

If HTTPS cert validation cannot be made correct but HTTP with the intended Host works, use an HTTP backend or fix the origin cert; never disable backend cert verification as the workaround.

If the origin already sends `Cache-Control` or `Expires` headers, no custom VCL is needed — Fastly respects these by default. Only add VCL snippets to override or extend caching behavior.

The full step-by-step workflow (create service, add domain, add backend, activate) is in the **fastly-cli** skill's services.md reference under "Create a Caching Proxy".

## Common VCL Recipes

Copy-pasteable patterns that are easy to get wrong without guidance.

### Grace Detection

`obj.ttl` is only meaningful in `vcl_hit`. Pass a flag to `vcl_deliver` via a request header.

```vcl
sub vcl_hit {
  if (obj.ttl <= 0s) {
    set req.http.X-Grace = "true";
  }
}

sub vcl_deliver {
  if (req.http.X-Grace) {
    set resp.http.X-Grace = "true";
  }
}
```

### Vary Header Append

**Warning: Set Vary in `vcl_fetch`, not `vcl_deliver`.** The Vary header must be present when the object enters the cache so the cache key includes the Vary dimensions. Setting Vary only in `vcl_deliver` means the cache won't differentiate responses — every user gets the same cached variant regardless of the Vary field.

Never `set beresp.http.Vary = "Accept-Encoding"` — that overwrites any existing Vary values from the origin, breaking other downstream caches.

```vcl
sub vcl_fetch {
  if (!beresp.http.Vary) {
    set beresp.http.Vary = "Accept-Encoding";
  } else if (beresp.http.Vary !~ "Accept-Encoding") {
    set beresp.http.Vary = beresp.http.Vary ", Accept-Encoding";
  }
}
```

### Redirect via Error

VCL has no `return(redirect)`. Use the synthetic error mechanism instead.

```vcl
sub vcl_recv {
  if (req.url ~ "^/old-path") {
    error 801 "https://example.com/new-path";
  }
}

sub vcl_error {
  if (obj.status == 801) {
    set obj.status = 301;
    set obj.http.Location = obj.response;
    synthetic {""};
    return(deliver);
  }
}
```

### Cache Status Headers

Use `obj.hits > 0` in `vcl_deliver` — this is the only reliable way to detect cache hits. Do not rely on auto-generated `resp.http.X-Cache` or any other header inspection. Pass PASS state from `vcl_recv` via a request header.

```vcl
sub vcl_recv {
  if (req.url ~ "^/api/") {
    set req.http.X-Pass = "true";

From fastly/fastly-agent-toolkit, MIT.

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