Internals¶
Overall Program Flow¶
AwsLimitChecker
provides the full and only public interface to this
project; it’s used by the awslimitchecker
command line script (entry point to runner
)
and should be the only portion directly used by external code.
Each AWS Service is represented by a subclass of the _AwsService
abstract base
class; these Service Classes are responsible for knowing which limits exist for the service they represent, what the
default values for these limits are, querying current limits from the service’s API (if supported),
and how to check the current usage via the AWS API (boto3
). When the
Service Classes are instantiated, they build a dict of all of their limits, correlating a string key (the “limit name”)
with an AwsLimit
object. The Service Class constructors must not make any network
connections; connections are created lazily as needed and stored as a class attribute. This allows us to inspect the
services, limits and default limit values without ever connecting to AWS (this is also used to generate the
Supported Limits documentation automatically).
All calls to boto3 client (“low-level”) methods that return a dict response that can
include ‘NextToken’ or another pagination marker, should be called through
paginate_dict()
with the appropriate parameters.
When AwsLimitChecker
is instantiated, it imports services
which in turn creates instances of all awslimitchecker.services.*
classes and adds them to a dict mapping the
string Service Name to the Service Class instance. These instances are used for all interaction with the services.
So, once an instance of AwsLimitChecker
is created, we should have instant access
to the services and limits without any connection to AWS. This is utilized by the --list-services
and
--list-defaults
options for the command line client.
Trusted Advisor¶
Attention
Trusted Advisor support in awslimitchecker is deprecated outside of the China and GovCloud regions, and now defaults to disabled/skipped in standard AWS, as the information available from TA can now be retrieved faster and more accurately via other means. See 10.0.0 (2020-12-07) for further information.
When AwsLimitChecker
is initialized, it also initializes an instance of
TrustedAdvisor
. In get_limits()
,
find_usage()
and check_thresholds()
, when called with
use_ta == True
(the default), update_limits()
is called on the TrustedAdvisor
instance.
update_limits()
polls Trusted Advisor data from the Support API via
_poll()
; this will retrieve the limits for all “flaggedResources” items in the
Service Limits
Trusted Advisor check result for the current AWS account. It then calls
_update_services()
, passing in the Trusted Advisor check results and the
dict of _AwsService
objects it was called with (from AwsLimitChecker
).
_update_services()
iterates over the Services in the Trusted Advisor check result
and attempts to find a matching _AwsService
(by string service name) in the dict passed
in from AwsLimitChecker
. If a match is found, it iterates over all limits for that service
in the TA result and attempts to call the Service
’s _set_ta_limit()
method.
If a matching Service is not found, or if _set_ta_limit
raises a ValueError (matching Limit not found
for that Service), an error is logged.
When AwsLimitChecker
initializes
TrustedAdvisor
, it passes in the
self.services
dictionary of all services and limits. At initialization time,
TrustedAdvisor
iterates all services
and limits, and builds a new dictionary mapping the limit objects by the return
values of their ta_service_name()
and ta_limit_name()
properties. This
allows limits to override the Trusted Advisor service and limit name that their
data comes from. In the default case, their service and limit names will be used
as they are set in the awslimitchecker code, and limits which have matching
Trusted Advisor data will be automatically populated.
In the TrustedAdvisor
class’s
_poll()
method,
_get_refreshed_check_result()
is used to retrieve the
check result data from Trusted Advisor. This method also implements the check
refresh logic. See the comments in the source code for the specific logic. There
are three methods of refreshing checks (refresh modes), which are controlled
by the ta_refresh_mode
parameter to TrustedAdvisor
:
- If
ta_refresh_mode
is the string “wait”, the check will be refreshed and awslimitchecker will poll for the refresh result every 30 seconds, waiting for the refresh to complete (or untilta_refresh_timeout
seconds have elapsed). This is exposed via the CLI as the--ta-refresh-wait
option. - If
ta_refresh_mode
is an integer, it will operate like the “wait” mode above, but only if the current result data for the check is more thanta_refresh_mode
seconds old. This is exposed via the CLI as the--ta-refresh-older
option. - If
ta_refresh_mode
is the string “trigger”, the check will be refreshed and the program will continue on immediately, without waiting for the refresh to complete; this will almost certainly result in stale check results in the current run. However, this may be useful if you desire to keepawslimitchecker
runs short, and run it on a regular schedule (i.e. if you runawslimitchecker
every 6 hours, and are OK with Trusted Advisor check data being 6 hours old). This is exposed via the CLI as the--ta-refresh-trigger
option.
Additionally, TrustedAdvisor
has a
ta_refresh_timeout
parameter. If this is set to a non-None
value (an integer),
refreshes of the check will time out after that number of seconds. If a timeout
occurs, a message will be logged at error level, but the program will continue
running (most likely using the old result data). This parameter is exposed via
the CLI as the --ta-refresh-timeout
option.
Important: It may take 30 to 60 minutes for the Service Limits check to refresh on large accounts. Please be aware of this when enabling the refresh options.
Using the check refresh options will require the trustedadvisor:RefreshCheck
IAM permission.
For use via Python, these same parameters (ta_refresh_mode
and ta_refresh_timeout
)
are exposed as parameters on the
AwsLimitChecker
constructor.
Service Quotas service¶
Unless use of Serivce Quotas is disabled with the --skip-quotas
command line option or by passing skip_quotas=False
to the AwsLimitChecker
constructor, awslimitchecker will retrieve all relevant data from the Service Quotas service. In the AwsLimitChecker
constructor (so long as skip_quotas
is True), an instance of the ServiceQuotasClient
class is constructed, passing in our boto3 connection keyword arguments for the current region. This client class instance is then passed to the constructor of every Service class (_AwsService
subclass) when the class is created, via the quotas_client
argument. Each _AwsService
class stores this as the _quotas_client
instance variable.
As the AwsLimitChecker
class iterates over all (configured) services in its get_limits()
, find_usage()
, and check_thresholds()
methods, it will call the service class’s _update_service_quotas()
method after calling update_limits()
and the service class’s _update_limits_from_api()
method (if present), and before the actual operation of getting limits, finding usage, or checking thresholds.
The _AwsService._update_service_quotas()
method will iterate through all limits (AwsLimit
) for the service and call the get_quota_value()
method for each. Assuming it returns a non-None
result, that result will be passed to the limit’s _set_quotas_limit()
method for later use in get_limit()
.
When retrieving values from Service Quotas, the ServiceCode
is taken from the _AwsService.quotas_service_code
attribute on the Service class. If that is set to None
, Service Quotas will not be consulted for that service. The ServiceCode
can also be overridden on a per-limit basis via the quotas_service_code
argument to the AwsLimit
constructor. The QuotaName
used by each limit defaults to the limit name itself (AwsLimit
instance variable name
) but can be overridden with the quota_name
argument to the AwsLimit
constructor.
Note that quota names are stored and compared in lower case.
Service API Limit Information¶
Some services provide API calls to retrieve at least some of the current limits, such as the DescribeAccountAttributes
API calls for RDS
and EC2. Services that
support such calls should make them in a _update_limits_from_api()
method, which will be automatically called from
get_limits()
. The _update_limits_from_api()
method should make the API call, and then
update all relevant limits via the AwsLimit
class’s _set_api_limit()
method.
Limit Value Precedence¶
The value used for a limit is the first match in the following list:
- Limit Override (set at runtime)
- API Limit
- Service Quotas
- Trusted Advisor
- Hard-coded default
Threshold Overrides¶
For more information on overriding thresholds, see
Python Usage / Setting a Threshold Override as well as the
documentation for AwsLimitChecker.check_thresholds()
and AwsLimitChecker.set_threshold_override()
.