Automated HTTP (microservices) supervisor
Epazote automatically update/add services specified in a file call
epazote.yml. Periodically checks the defined endpoints and execute recovery commands in case services responses are not behaving like expected helping with this to automate actions in order to keep services/applications up and running.
In Continuous Integration/Deployment environments the file
epazote.yml can dynamically be updated/change without need to restart the supervisor, avoiding with this an extra dependency on the deployment flow which could imply to restart the supervisor, in this case Epazote.
How it works
In its basic way of operation, Epazote periodically checks the services endpoints “URLs” by doing an HTTP GET Request, based on the response Status code, Headers or either the body, it executes a command.
In most scenarios, is desired to apply a command directly to the application in cause, like a signal (
kill -HUP), or either a restart (
sv restart app), therefore in this case Epazote and the application should be running on the same server.
Epazote can also work in a standalone mode by only monitoring and sending alerts if desired.
How to use it
To compile from source, after downloading the sources use
maketo build the binary
Epazote was designed with simplicity in mind, as an easy tool for DevOps and as a complement to infrastructure orchestration tools like Ansible and SaltStack, because of this YAML is used for the configuration files, avoiding with this, the learn of a new language or syntax and simplifying the setup.
services: google: url: https://www.google.com seconds: 5 expect: status: 302 ssl: hours: 72 if_not: cmd: echo -n "google down"
$ epazote -f /path/to/yaml/file/basic.yml -d
-d is for debugging, will print all output to standard output.
This basic setup will supervise every 5 seconds the service with name
http://www.google.com and will expect an
302 Status code if not, it will
echo -n "google down"
ssl: hours: 72 means to send an alert if the certificate is about to expire in the next 72 hours.
Extending the basic example for receiving notifications:
config: smtp: username: [email protected] password: password server: mail.example.com port: 587 headers: from: [email protected] to: [email protected] subject: "[name - exit- status]" services: google: url: http://www.google.com minutes: 3 expect: status: 200 if_not: cmd: echo -n "google down" notify: yes
In this case, every 3 minutes the service will be checked and in case of not receiving a
200 Status code, besides executing the command:
echo -n "google down" an email is going to be send to
[email protected], this because of the
notify: yes setting.
The configuration file
The configuration file (YAML formated) consists of two parts, a config and a services (Key-value pairs).
The config section
The config section is composed of:
- smtp (Email settings for sending notification) - scan (Paths used to find the file 'epazote.yml')
config: smtp: username: [email protected] password: password server: mail.example.com port: 587 headers: from: [email protected] to: [email protected] [email protected] [email protected] subject: "[_name_, _because_]" scan: paths: - /arena/home/sites - /home/apps minutes: 5
config – smtp
Required to properly send alerts via email, all fields are required, the
headers section can be extended with any desired key-pair values.
config – smtp – subject
The subject can be formed by using this keywords:
_url_ on the previous example,
subject: [_name_, _status_] would transform to
[my service - 500] the
name has replaced by the service name,
my service and
status by the response status code
500 in this case.
config – scan
Paths to scan every N
hours, a search for services specified in a file call
epazote.yml is made.
The scan setting is optional however is very useful when doing Continues Deployments. for example if your code is automatically uploaded to the directory
/arena/home/sites/application_1 and your scan paths contain
/arena/home/sites, you could simple upload on your application directory a file named
epazote.yml with the service rules, thus achieving the deployment of your application and the supervising at the same time.
As you may notice the
config section contains mainly settings for sending alerts/notifications apart from the
scan setting, therefore is totally optional, meaning that Epazote can still run and check your services without the need of the
If you want to automatically update/load services you will need the
config - scan setting.
The services section
Services are the main functionality of Epazote, is where the URL’s and the rules based on the response are defined, since options vary from service to service, an example could help better to understand the setup:
services: my service 1: url: http://myservice.domain.tld/_healthcheck_ timeout: 5 seconds: 60 log: http://monitor.domain.tld expect: status: 200 header: content-type: application/json body: find this string on my site if_not: cmd: sv restart /services/my_service_1 notify: [email protected] msg: | line 1 bla bla line 2 if_status: 500: cmd: reboot 404: cmd: sv restart /services/cache msg: restarting cache notify: [email protected] [email protected] if_header: x-amqp-kapputt: cmd: restart abc notify: [email protected] msg: | The rabbit is angry & hungry x-db-kapputt: cmd: svc restart /services/db other service: url: https://self-signed.ssl.tld/ping header: Origin: http://localhost Accept-Encoding: gzip insecure: true minutes: 3 redirect service: url: http://test.domain.tld/ follow: yes hour: 1 expect: status: 302 if_not: cmd: service restart abc notify: yes emoji: 1F600-1F621 salt-master: test: pgrep -f salt if_not: cmd: service restart salt_master notify: [email protected]
services – name of service (string)
An unique string that identifies your service, in the above example, there are 3 services named:
- my service 1
- other service
- redirect service
services – url (string)
URL of the service to supervise
services – follow (boolean true/false)
By default if a 302 Status code is received, Epazote will not follow it, if you would like to follow all redirects, this setting must be set to true.
services – insecure (boolean true/false)
This option explicitly allows Epazote to perform “insecure” SSL connections. It will disable the certificate verification.
services – stop (int)
Defines the number or times the
cmd will be executed, by default the
cmd is executed only once, with the intention to avoid indefinitely loops. If value is set to
cmd never stops. defaults to 0,
stop 2 will execute “0, 1, 2” (3 times) the
services – timeout in seconds (int)
Timeout specifies a time limit for the HTTP requests, A value of zero means no timeout, defaults to 5 seconds.
services – retry_limit (int)
Specifies the number of times to retry an request, defaults to 3.
services – retry_interval (int)
Specifies the time between attempts in milliseconds. The default value is 500 (0.5 seconds).
services – read_limit (int)
N number of bytes instead of the full body. This helps to make a more “complete” request and avoid getting an HTTP status code [408 when testing aws ELB](http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/ts-el b-error-message.html#ts-elb-errorcodes-http408).
services – seconds, minutes, hours
How often to check the service, the options are: (Only one should be used)
- seconds N
- minutes N
- hours N
N should be an integer.
services – log (URL)
An URL to post all events, default disabled.
services – expect
expect block options are:
- status (int)
- header (key, value)
- body (regular expression)
- if_not (Action block)
services – expect – status
An Integer representing the expected HTTP Status Code
services – expect – header (start_with match)
A key-value map of expected headers, it can be only one or more.
The headers will be considered valid if they starts with the required value, for example if you want to check for
Content-type: application/json; charset=utf-8 you can simple do something like:
header: Content-Type: application/json
This helps to simplify the matching and useful in cases where the headers changes, for example:
Content-Range: bytes 100-64656926/64656927 can be matched with:
header: Content-Range: bytes
services – expect – body
A regular expression used to match a string on the body of the site, use full in cases you want to ensure that the content delivered is always the same or keeps a pattern.
services – expect (How it works)
expect logic tries to implement a if-else logic
body are the if and the
if_not block becomes the else.
if status header body else: if_not
In must cases only one option is required, check on the above example for the service named “redirect service”.
In case that more than one option is used, this is the order in how they are evaluated, no meter how they where introduced on the configuration file:
1. body 2. status 3. header
The reason for this order is related to performance, at the end we want to monitor/supervise the services in an efficient way avoiding to waste extra resources, in must cases only the HTTP Headers are enough to take an action, therefore we don’t need to read the full body page, because of this if no
body is defined, Epazote will only read the Headers saving with this time and process time.
services – expect – if_not
if_not is a block with an action of what to do it we don’t get what we where expecting (
expect). See services – Actions
services – if_status & if_header
There maybe cases in where third-party dependencies are down and because of this your application could not be working properly, for this cases the
if_header could be useful.
For example if the database is your application could start responding an status code 500 or either a custom header and based on does values take execute an action:
The format for
if_status is a key-pair where key is an int representing an HTTP status code, and the value an Action option
The format for
if_header is a key-pair where key is a string of something you could relate/match and has in other if_X conditions, value is an Action.
This are the only
if's and the order of execution:
This means that if a service uses
if_not, it will evaluate first the
if_status and execute an Action if required, in case an
if_header are set, same applies, first is evaluated
if_header and last
services – Actions
An Action has five options:
They can be used all together, only one or either none.
services – Actions – cmd (string)
cmd Contains the command to be executed.
services – Actions – notify (string)
notify Should contain
yes, the email email address or addresses (space separated) of the recipients that will be notified when the action is executed.
If the string is
yes the global recipients will be used.
services – Actions – msg (list)
msg: - send this if exit 0 (all OK) - send this if exit 1 (something is wrong)
Based on the exit status either msg or msg is used,
services – Actions – emoji (list)
emoji Unicode characters to be used in the subject, example:
emoji: - 1F600 - 1F621
If services are OK they will use the first
1F600 if not they will use
1F621, if set to
0 no emoji will be used. The idea behind using unicode/emoji is to cough attention faster and not just ignore the email thinking is spam.
service – Actions – http (list(key, value))
A custom URL to GET/POST depending on the exit status, example:
http: - url: "https://api.hipchat.com/v1/rooms/message?auth_token=your_token&room_id=7&from=Alerts&message=service+OK+_name_+_because_" - url: "https://api.hipchat.com/" header: Content-Type: application/x-www-form-urlencoded data: | room_id=10&from=Alerts&message=_name_+exit+code+_exit_ method: POST
When a service fails or returns an exit 1 the second url
https://api.hipchat.com/ with method
POST and the custom
data will be used, notice that all the ocurances on the data that are within an
_(key)_ will be replaced with the corresponding value, in this case:
will be replaced with:
When recovery the first url will be used, in this case will be a GET instead of a post, so:
notice that the name, exit, because are been replaced with the values of name, exit, because of the service.
services – Test
Epazote It is mainly used for HTTP services, for supervising other applications that don’t listen or accept HTTP connections, like a database, cache engine, etc. There are tools like daemontools, runit as already mentioned, even so, Epazote can eventually be used to execute an action based on the exit of a command for example:
salt-master: test: pgrep -f salt if_not: cmd: service restart salt_master notify: [email protected]
In this case:
test: pgrep -f salt will execute the
cmd on the
if_not block in case the exit code is > 0, from the
pgrep man page:
EXIT STATUS The pgrep and pkill utilities return one of the following values upon exit: 0 One or more processes were matched. 1 No processes were matched. 2 Invalid options were specified on the command line. 3 An internal error occurred.
green dots give some comfort — Because of this when using the
log option an extra service could be configure as a receiver for all the post that Epazote produce and based on the data obtained create a custom dashboard, something similar to: https://status.cloud.google.com/ or http://status.aws.amazon.com/
Please report any problem, bug, here: https://github.com/nbari/epazote/issues