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45. Configuration reference

45.1. The devlove.yaml file

ShimmerCat QS uses two instance-wide configuration files, both of which are expected to be at fixed locations relative to the server’s working directory:

  • devlove.yaml contains basic configuration about which domains to serve.

  • <scratch-folder>/tweaks.yaml contains technical settings that can be changed to balance security and features.

The basic features of this file are covered in detail in our tutorials in this documentation. Here is the full reference for the file, using json-schema, though we have used YAML instead of JSON for the schema so that it is easier to read. Scroll to after the text-box to find additional information about each object.

---
title: ShimmerCatDevlove
$schema: http://json-schema.org/draft-04/schema#
type: object
properties:
    shimmercat-devlove:
      type: object
      properties:
        domains: 
          type: object
          minProperties: 1
          patternProperties:
            "elec +[a-zA-Z0-9.-]+": 
                $ref: "#/definitions/electricDomain"
            "api +[a-zA-Z0-9.-]+":
                $ref: "#/definitions/apiDomain"
          additionalProperties: false
      required: ["domains"]
additionalProperties: false
required: ["shimmercat-devlove"]
definitions:
  electricDomain:
    type: object
    title: ElectricDomain
    properties:
      root-dir:
        oneOf:
          - type: string
          - $ref: "#/definitions/rootDirUseConsultant"
          - $ref: "#/definitions/rootDirFetchBackend"
      views-dir:
        type: string
      consultant:
        $ref: "#/definitions/consultant"
      consultants:
        type: object
        additionalProperties:
          $ref: "#/definitions/consultant"
      cache-key:
        type: string
      change-url:
        type: array
        items:
          - type: string
      changelist-settings:
        type: object
        properties:
          tNew:
             type: number
          tOld:
             type: number
        required: ["tNew", "tOld"]
      prob-accelerator-kicks-in:
        type: number
      bot-protection-enabled:
        type: boolean
    required: 
      - "root-dir"
    additionalProperties: false
  apiDomain:
    type: object
    title: ApiDomain
    properties:
      port:
        $ref: "#/definitions/networkAddress"
    required: 
      - port
  applicationPort:
    type: object 
    title: ApplicationPort
    properties:
      # TO-DO: We can make the `connect-to` property more precise
      "connect-to":
        $ref: "#/definitions/networkAddress"
      "document-root":
        type: string
      "application-protocol":
        type: string 
        pattern: |
          fastcgi|fcgi|http|http11|HTTP/1\.1|HTTP
      "encryption-level":
        type: string
        pattern: |
          plain|tls 
      "timeouts": 
        $ref: "#/definitions/applicationLifecycleTimeouts"
      "use-host":
        type: string
      "forward-error-pages":
        type: boolean
      "enable-ip-records":
        type: boolean
      "change-headers-in":
        type: boolean
      "change-headers-out":
        type: boolean
    required: ["connect-to"]
  networkAddress:
      type: string 
      pattern: "^(((lookup\\([a-zA-Z0-9.-]+\\))|([0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+))?:)?([0-9]+)$"
  applicationLifecycleTimeouts:
      type: object
      title: Application Lifecycle Timeouts
      properties:
        # Will add more, like "connection" and "handshake" later
        "inactivity":
           type: "number"
        "connection":
           type: "number"
        "handshake":
           type: "number"
  consultants:
      type: object
      additionalProperties:
        $ref: "#/definitions/applicationPort"
  consultant:
      oneOf:
        - $ref: "#/definitions/networkAddress"
        - $ref: "#/definitions/applicationPort"
  rootDirUseConsultant:
      type: object
      properties:
        "use-consultant":
          type: string
      additionalProperties: false
      required:
        - "use-consultant"
  rootDirFetchBackend:
      type: object
      properties: 
        "fetch-backend":
          type: string
        "http-port":
          $ref: "#/definitions/networkAddress"
        "use-host":
          type: string
        "concurrency-limit":
          type: number
        "path-prefix":
          type: string
      required: 
        - "fetch-backend"
        - "use-host"

The following sub-sections explain the objects defined in the schema above.

45.1.1. Top objects

The top object in the devlove.yaml should only contain one property, shimmercat-devlove, and right below it another property domains:

---
shimmercat-devlove:
  domains: 
    ...

domains should contain an object, with one property for each domain served by ShimmerCat.

45.1.2. Domains

The contents of the domains object are two types of domains: file-serving domains, which we call electric, and pure-forwarding domains, which we call api domains (using lowercase for “api”).

Electric domains can be recognized automatically by the subkeys root-dir or consultant. Like this:

shimmercat-devlove:
    domains:
        www.mysite.com:
            root-dir: www

They can also be distinguished by prefixing the word elec to the key with the domain name.

API domains can be recognized automatically by specifying the subkey port with the web application port to which ShimmerCat should proxy requests, or by prefixing the word api to the key with the domain name, like this:

shimmercat-devlove:
    domains:
        api my-api.mysite.com:
            port: "8080"

Note that the value of the port property should follow the network-address schema, described below.

Of course, you can mix and match domains of different types in a single devlove.yaml file. Like this:

shimmercat-devlove:
    domains:
        api1.mysite.com:
            port: "8080"
        www.mysite.com:
            root-dir: www

What follow are all properties of the electric domains.

45.1.3. The root-dir

This is a string denoting a directory with static assets to serve on the domain. Or an object, describing an equivalent mean to obtain the assets. ShimmerCat QS, being a caching server, will just read the files from this place as they are requested by website visitors and copy-and-process them to its internal cache in the scratch folder. This means that you can mount a high latency filesystem and use it as your root-dir, and still obtain a very fast website.

This is the only mandatory property in an electric domain configuration object.

45.1.4. The views-dir

This is where views are expected to be. If left unspecified and root-dir is a string, then the root-dir will be used. Note that view files are expected to be in a local filesystem, since at best they are just cached for a few seconds.

45.1.5. Consultant(s)

In ShimmerCat lingo, a consultant is an external application that provides either contents or base data to create contents (depending on the content-disposition). In the first case “consultant” is synonymous to “origin” and “application backend”.

A single domain can access more than one consultant, via the consultants property of the domain configuration object. For example:

...
       consultants:
          my-php-app:
            ...
          my-node-js-app:
            ...

The snippet above defines two consultants with names my-php-app and my-node-js-app, both of which can be served in the same domain. Their names can be used in a view to decide where to forward a request to.

Whenever a consultant is needed but no consultant name is provided, ShimmerCat QS fills in the missing name with default, and tries to use that one.

The property consultant, the singular of consultants, is just a shortcut to

       consultants:
          default: 
             ...

Consultants configuration also includes the following properties:

  • document-root: passed as DOCUMENT_ROOT to FastCGI application

  • connect-to: the application port where to connect to the service. It follows the standard network port syntax. This is the only required property.

  • application-protocol: one of fastcgi or http, to denote FastCGI or HTTP 1.1. This is the expected protocol to talk to the backend. When not specified, ShimmerCat tries to guess.

  • encryption-level: either plain or tls. ShimmerCat uses plain by default.

  • timeouts: different timeouts for contacting the application backend.

  • use-host: Optional. If specified, it should be a string to use as the value of the Host HTTP 1.1 header; also used for the HTTP_HOST FastCGI field. Useful in those cases when one needs to replace the host header in outgoing requests. Otherwise outgoing requests go with the same Host header value that came in the original request.

45.2. Command Line Reference

45.2.1. Command line options across modes

ShimmerCat, as of version 1.5.0 has two public-facing modes of operation: devlove and Internet The modes have slightly different options, and some of them have different defaults across modes.

  • devlove: a handy option to run while developing. It enables SOCKS5 by default, relaxes security settings and strives to rely as much information as possible to web developers.

  • internet: an option to run when facing the Internet. It disables SOCKS5 by default, tightens security settings and strives for reliability and stability. In this mode ShimmerCat runs a master process and a number of workers.

In addition, there are two non-public modes:

  • worker: this mode is used automatically by the worker processes spawned in internet mode.

  • changelist-daemon: used to keep the cache fresh.

In any of the modes, you can see which options ara available via the --help sub-option:

$ shimmercat devlove --help
A mode for web developers
...

45.2.2. General options

  • --listen, -l: Network address to bind to. It has several supported formats. If given as an integer port-no, it will bind to that port at the localhost interface 127.0.0.1 (not to 0.0.0.0). It can also be given as a pair ip-number:port-no, in which case it will bind to that ip address and port, or as unix://<abs-or-rel-path, in which case the server will bind to a local Unix socket. This last choice may come handy for different proxy-ing setups.

  • --socks5-listen, -5: Port where to bind the SOCKS5 proxy. Accepts the same formats than the --listen option.

  • --s5-forward, -w: Instructs the SOCKS5 built-in proxy to forward connections which are not handled by local domains. For example, if your devlove.yaml file specifies that www.mysite.com should be served locally, but you have URLs referencing an external site like fonts.google.com, this option will “pass-through” connections to the later domain. Without this option, those connections are blocked.

  • --scratch-dir-name: The name of the scratch directory. By default, it is “.shimmercat.loves.devs”. The scratch directory contains the Redis database that ShimmerCat uses for internal comunications and caching, the local filesystem socket to Redis and the cache of representations.

  • --worker-count: How many workers to span. This option is available only in internet mode.

  • --disable-socks-5: Disable SOCKS5. Use this option for enhanced security if you are abusing devlove mode to serve an actual website. We recommend you to upgrade instead.

  • --enable-socks-5: Use this option to enable SOCKS5 in internet mode.

  • --wait-for-redis-to-start: Time in milliseconds to wait for Redis to start. By default, ShimmerCat makes a short pause of 50 milliseconds before trying to connect to Redis. That is enough in most modern hardware, but in old hardware or in otherwise throttled down CPUs Redis may take longer to start. Use this option in those cases.

  • --working-dir: Directory that ShimmerCat should consider as current. This is entirely equivalent to starting ShimmerCat at that directory.

  • --log-codes: Command line option used to specify what to log. For example, --log-codes=all\\connection can be used to enable all the logs minus logs related to connections. For more details, read the page on logging.

  • --http2https, -t: Gives ShimmerCat a port to make HTTP to HTTPS redirects. For details, see the corresponding section in the Internet mode article.

45.2.3. Options for development

The following options are handy to debug protocol-specific issues:

  • --disable-http-11: Disable HTTP/1.1. That is, only accept HTTP/2 connections.

  • --disable-http-2: Disable HTTP/2, that is, only accept HTTP/1.1 connections.

When developing a website, it is handy at times to disable all cache directives or even HTTP/2 Push. These two options are for that:

  • --disable-ua-caching: Changes the cache headers to ask the browser not to cache any requests, for all requests in all virtual domains ran by the server. In particular, this removes the etag header and changes the cache-control header to no-cache, no-store, max-age=0, private.

  • --disable-push: Disables HTTP/2 Push in all virtual domains ran by the server. Notice that that otherwise ShimmerCat respects the connection settings indicated by the client as part of a SETTINGS frame.

  • --show-proxied-headers: Shows the headers which are forwarded to an inner application, and the headers which are received by that application.

  • --sim-bandwidth: Part of the network simulator. Limits server bandwidth for a single HTTP/2 connection to the number given here. If you don’t specify a unit, the server will assume bytes per second as the unit. Units accepted are a subset of the units described at Wikipedia’s page: kbit/s, kb/s (kilobits per second), Mb/s, Mbit/s (megabits per second), Kibit/s (kibits per second), Mibit/s (mibits per second), kB/s (kylobytes per second) and MB/s (megabytes per second). Example: --sim-bandwidth=100kb/s.

  • --sim-latency: Part of the network simulator. Adds latency to packets in their way out, by delaying them by the amount of time specified in this option. If no units are specified, ShimmerCat assumes that the time is given in seconds and fractions of a second. Two units are allowed here, s and ms. Example: --sim-latency=110ms.