codecrunchers/js-poll-ssm

Poll an AWS Parameter Store for changing Key/Values

Dynamic Application Config for NodeJS Apps

Avoid redeploying your NodeJS app on AWS just to avail of new paramaters/config values.

In production, at runtime, resources outside our control may require that we adapt to these events.

Some examples:

• Our data provider chnages a URL
• We need to change the poll timeout on a connection
• Our thread pool size has to be altererd
• Query timeouts need to be extended due to load
• An API Token is updated

This is available via the excellent Netflix Hystrix, but not for JavaScript/Node.

In a lot of environments this requires a redepoly of an application; as these values are often embedded in the app at deploy time / compile time in the form of Environemt variables or config file. They are read once and persist until an application restarts.

No code changing then we should not have to redeploy.

This pattern is described in 'Release It' - a must read bible for the professional software engineer.

So now you're faced with a full pipeline release cycle, canary releases to perform that downtime free deplyoment - but there are no code changes, just config. Time to separate that out..

Decouple from config

It doesn't need to be this way - all you need is a value changed - this module addresses this by polling a Config store, be it:

• AWS SSM
• Redis [TODO]
• Consul [TODO]

and updating the value of your Env vars

Starting it up

• 1 Set your provider, curretly only AWS works: PROVIDER_TYPE='aws'
• 2 Export AWS_ACCESS_KEY_ID='your key'
• 3 Export AWS_SECRET_ACCESS_KEY='your key'
• 4 Export your key prefix, this is the unique app path to be searched: KEY_PREFIX=/my/app/hola-mundo/ (All keys under that 'namespace' will be set as Env vars)
• 5 Export your gobal key prefix, this is for shared app params: GLOBAL_KEY_PREFIX=/my/apps/globals/
• 6 Export POLL_TIME set a poll timer for the refresh

LOG_LEVEL=debug NODE_ENV=development node src/index.js