Class: Fog::Cache
- Inherits:
-
Object
- Object
- Fog::Cache
- Defined in:
- lib/fog/core/cache.rb
Overview
A generic cache mechanism for fog resources. This can be for a server, security group, etc.
Currently this is a on-disk cache using yml files per-model instance, however there is nothing in the way of extending this to use various other cache backends.
Basic functionality
set the namespace where this cache will be stored:
Fog::Cache.namespace_prefix = “service-account-foo-region-bar”
cache to disk:
# after dumping, there will be a yml file on disk:
resouce.cache.dump
# you can load cached data in from a different session
Fog::Cache.load(Fog::Compute::AWS::Server, compute)
# you can also expire cache (removes cached data assocaited with the resources of this model associated to the service passed in).
Fog::Cache.expire_cache!(Fog::Compute::AWS::Server, compute)
More detailed flow/usage
Normally, you would have a bunch of resources you want to cache/reload from disk. Every fog model has a cache
object injected to accomplish this. So in order to cache a server for exmaple you would do something like this:
# note this is necessary in order to segregate usage of cache between various providers regions and accounts.
# if you are using one account/region/etc only, you still must set it. 'default' will do.
Fog::Cache.namespace_prefix = "prod-emea-eu-west-1"
s = security_groups.sample; s.name # => "default"
s.cache.dump # => 2371
Now it is on disk:
shai@adsk-lappy ~ % tree ~/.fog-cache/prod-emea-eu-west-1/
/Users/shai/.fog-cache/prod-emea-eu-west-1/
└── fog_compute_aws_real
└── fog_compute_aws_securitygroup
├── default-90928073d9d5d9b4e7545e88aee7ec4f.yml
You can do the same with a SecurityGroup, Instances, Elbs, etc.
Note that when loading cache from disk, you need to pass the appropriate model class, and service associated with it. Service
is passed in is so that the service/connection details can be loaded into the loaded instances so they can be re-queried, etc. Model
is passed in so we can find the cache data associated to that model in the namespace of cache this session is using: Will try to load all resources associated to those. If you had 1 yml file, or 100, it would load whatever it could find. As such, the normal usage of dumping would be do it on a collection:
load_balancers.each {|elb| elb.cache.dump }
In order to load the cache into a different session with nothing but the service set up, use like so: As mentioned, will load all resources associated to the model_klass
and service
passed in.
instances = Fog::Cache.load(Fog::Compute::AWS::Server, compute)
instances.first.id # => "i-0569a70ae6f47d229"
Note that if there is no cache located for the model
class and service
passed to ‘Fog::Cache.load` you will get an exception you can handle (for example, to load the resources for the fisrt time):
Fog::Cache.expire_cache!(Fog::Compute::AWS::SecurityGroup, compute)
# ... now there is no SecurityGroup cache data. So, if you tried to load it, you would get an exception:
Fog::Cache.load(Fog::Compute::AWS::SecurityGroup, compute)
rescue Fog::Cache::CacheNotFound => e
puts "could not find any cache data for security groups on #{compute}"
get_resources_and_dump
Extending cache backends
Currently this is on-disk using yml. If need be, this could be extended to other cache backends:
Find references of yaml in this file, split out to strategy objects/diff backends etc.
Defined Under Namespace
Classes: CacheDir, CacheNotFound
Constant Summary collapse
- SANDBOX =
where different caches per
service
api keys, regions etc, are stored see thenamespace_prefix=
method. ENV["HOME"] ? File.("~/.fog-cache") : File.(".fog-cache")
Instance Attribute Summary collapse
-
#model ⇒ Object
readonly
when a resource is used such as ‘server.cache.dump` the model klass is passed in so that it can be identified from a different session.
Class Method Summary collapse
-
.clean! ⇒ Object
cleans the ‘SANDBOX` - specific any resource cache of any namespace, and any metadata associated to any.
-
.const_get_compat(strklass) ⇒ Object
:nodoc: compatability for 1.8.7 1.9.3.
-
.create_namespace(model_klass, service) ⇒ Object
creates on-disk cache of this specific
model_klass
and @service. -
.expire_cache!(model_klass, service) ⇒ Object
Expires cache - this does not expire all cache associated.
-
.load(model_klass, service) ⇒ Object
Loads cache associated to the
model_klass
andservice
into memory. -
.load_cache(path) ⇒ Object
loads yml cache from path on disk, used to initialize Fog models.
-
.metadata ⇒ Object
retrive metadata for this
namespace
of cache. -
.namespace(model_klass, service) ⇒ Object
The path/namespace where the cache is stored for a specific
model_klass
and @service. - .namespace_prefix ⇒ Object
- .namespace_prefix=(name) ⇒ Object
- .safe_path(klass) ⇒ Object
-
.uniq_w_block(arr) ⇒ Object
:nodoc: compatability for 1.8.7 1.9.3.
-
.valid_for_load?(path) ⇒ Boolean
method to determine if a path can be loaded and is valid fog cache format.
-
.write_metadata(h) ⇒ Object
write any metadata -
hash
information - specific to the namespaced cache in the session.
Instance Method Summary collapse
-
#dump ⇒ Object
Dump a Fog::Model resource.
-
#dump_to ⇒ Object
the location of where to save this fog model/instance to.
-
#initialize(model) ⇒ Cache
constructor
A new instance of Cache.
Constructor Details
#initialize(model) ⇒ Cache
Returns a new instance of Cache.
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# File 'lib/fog/core/cache.rb', line 260 def initialize(model) @model = model end |
Instance Attribute Details
#model ⇒ Object (readonly)
when a resource is used such as ‘server.cache.dump` the model klass is passed in so that it can be identified from a different session.
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# File 'lib/fog/core/cache.rb', line 98 def model @model end |
Class Method Details
.clean! ⇒ Object
cleans the ‘SANDBOX` - specific any resource cache of any namespace, and any metadata associated to any.
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# File 'lib/fog/core/cache.rb', line 192 def self.clean! FileUtils.rm_rf(SANDBOX) end |
.const_get_compat(strklass) ⇒ Object
:nodoc: compatability for 1.8.7 1.9.3
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# File 'lib/fog/core/cache.rb', line 146 def self.const_get_compat(strklass) # https://stackoverflow.com/questions/3163641/get-a-class-by-name-in-ruby strklass.split('::').inject(Object) do |mod, class_name| mod.const_get(class_name) end end |
.create_namespace(model_klass, service) ⇒ Object
creates on-disk cache of this specific model_klass
and @service
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# File 'lib/fog/core/cache.rb', line 180 def self.create_namespace(model_klass, service) FileUtils.mkdir_p(self.namespace(model_klass, service)) end |
.expire_cache!(model_klass, service) ⇒ Object
Expires cache - this does not expire all cache associated. Instead, this will remove all on-disk cache of this specific model_klass
and and @service
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# File 'lib/fog/core/cache.rb', line 186 def self.expire_cache!(model_klass, service) FileUtils.rm_rf(namespace(model_klass, service)) end |
.load(model_klass, service) ⇒ Object
Loads cache associated to the model_klass
and service
into memory.
If no cache is found, it will raise an error for handling:
rescue Fog::Cache::CacheNotFound
set_initial_cache
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# File 'lib/fog/core/cache.rb', line 107 def self.load(model_klass, service) cache_files = Dir.glob("#{namespace(model_klass, service)}/*") raise CacheNotFound if cache_files.empty? # collection_klass and model_klass should be the same across all instances # choose a valid cache record from the dump to use as a sample to deterine # which collection/model to instantiate. sample_path = cache_files.detect{ |path| valid_for_load?(path) } model_klass = const_get_compat(load_cache(sample_path)[:model_klass]) collection_klass = const_get_compat(load_cache(sample_path)[:collection_klass]) if load_cache(sample_path)[:collection_klass] # Load the cache data into actual ruby instances loaded = cache_files.map do |path| model_klass.new(load_cache(path)[:attrs]) if valid_for_load?(path) end.compact # Set the collection and service so they can be reloaded/connection is set properly. # See https://github.com/fog/fog-aws/issues/354#issuecomment-286789702 loaded.each do |i| i.collection = collection_klass.new(:service => service) if collection_klass i.instance_variable_set(:@service, service) end # uniqe-ify based on the total of attributes. duplicate cache can exist due to # `model#identity` not being unique. but if all attributes match, they are unique # and shouldn't be loaded again. uniq_loaded = uniq_w_block(loaded) { |i| i.attributes } if uniq_loaded.size != loaded.size Fog::Logger.warning("Found duplicate items in the cache. Expire all & refresh cache soon.") end # Fog models created, free memory of cached data used for creation. @memoized = nil uniq_loaded end |
.load_cache(path) ⇒ Object
loads yml cache from path on disk, used to initialize Fog models.
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# File 'lib/fog/core/cache.rb', line 198 def self.load_cache(path) @memoized ||= {} return @memoized[path] if @memoized[path] @memoized[path] = YAML.load(File.read(path)) end |
.metadata ⇒ Object
retrive metadata for this namespace
of cache. returns empty {} if none found.
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# File 'lib/fog/core/cache.rb', line 237 def self. mpath = File.join(SANDBOX, namespace_prefix, "metadata.yml") if File.exist?(mpath) = YAML.load(File.read(mpath)) return else return {} end end |
.namespace(model_klass, service) ⇒ Object
The path/namespace where the cache is stored for a specific model_klass
and @service.
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# File 'lib/fog/core/cache.rb', line 248 def self.namespace(model_klass, service) raise CacheDir.new("Must set an explicit identifier/name for this cache. Example: 'serviceX-regionY'") unless namespace_prefix ns = File.join(SANDBOX, namespace_prefix, service.class.to_s, model_klass.to_s) ns = safe_path(ns) end |
.namespace_prefix ⇒ Object
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# File 'lib/fog/core/cache.rb', line 208 def self.namespace_prefix @namespace_prefix end |
.namespace_prefix=(name) ⇒ Object
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# File 'lib/fog/core/cache.rb', line 204 def self.namespace_prefix=(name) @namespace_prefix = name end |
.safe_path(klass) ⇒ Object
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# File 'lib/fog/core/cache.rb', line 256 def self.safe_path(klass) klass.to_s.gsub("::", "_").downcase end |
.uniq_w_block(arr) ⇒ Object
:nodoc: compatability for 1.8.7 1.9.3
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# File 'lib/fog/core/cache.rb', line 154 def self.uniq_w_block(arr) ret, keys = [], [] arr.each do |x| key = block_given? ? yield(x) : x unless keys.include? key ret << x keys << key end end ret end |
.valid_for_load?(path) ⇒ Boolean
method to determine if a path can be loaded and is valid fog cache format.
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# File 'lib/fog/core/cache.rb', line 167 def self.valid_for_load?(path) data = load_cache(path) if data && data.is_a?(Hash) if [:identity, :model_klass, :collection_klass, :attrs].all? { |k| data.keys.include?(k) } return true else Fog::Logger.warning("Found corrupt items in the cache: #{path}. Expire all & refresh cache soon.\n\nData:#{File.read(path)}") return false end end end |
.write_metadata(h) ⇒ Object
write any metadata - hash
information - specific to the namespaced cache in the session.
you can retrieve this in other sessions, as long as namespace_prefix
is set you can overwrite metadata over time. see test cases as examples.
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# File 'lib/fog/core/cache.rb', line 216 def self.(h) if namespace_prefix.nil? raise CacheDir.new("Must set an explicit identifier/name for this cache. Example: 'serviceX-regionY'") unless namespace_prefix elsif !h.is_a?(Hash) raise CacheDir.new("metadta must be a hash of information like {:foo => 'bar'}") end mpath = File.join(SANDBOX, namespace_prefix, "metadata.yml") to_write = if File.exist?(mpath) YAML.dump(YAML.load(File.read(mpath)).merge!(h)) else YAML.dump(h) end mdir = File.join(SANDBOX, namespace_prefix) FileUtils.mkdir_p(mdir) if !File.exist?(mdir) File.open(mpath, "w") { |f| f.write(to_write) } end |
Instance Method Details
#dump ⇒ Object
Dump a Fog::Model resource. Every fog model/instance now has a cache
method/object injected in. as such you can use the #dump method to save the attributes and metadata of that instance as cache which can be re-used in some other session.
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# File 'lib/fog/core/cache.rb', line 267 def dump if !File.exist?(self.class.namespace(model.class, model.service)) self.class.create_namespace(model.class, model.service) end data = { :identity => model.identity, :model_klass => model.class.to_s, :collection_klass => model.collection && model.collection.class.to_s, :attrs => model.attributes } File.open(dump_to, "w") { |f| f.write(YAML.dump(data)) } end |
#dump_to ⇒ Object
the location of where to save this fog model/instance to.
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# File 'lib/fog/core/cache.rb', line 281 def dump_to # some fog models have an identity field that is duplicate. # duplicate identities can mean the cache for that already exists. # this means cache duplication is possible. # # see "dumping two models that have duplicate identity" test case. "#{self.class.namespace(model.class, model.service)}/#{model.identity}-#{SecureRandom.hex}.yml" end |