await

Await availability of resources.

This can be useful in the context of Docker Compose where a service needs to wait for other dependent services.

Optionally a timeout can be provided to specify how long to wait for all dependent resources to become available. On success the command returns code 0, on failure it returns code 1.

Additionally a command can be specified which gets executed after all dependent resources became available.

Installation

go get -u github.com/betalo-sweden/await

or

curl -s -f -L -o await https://github.com/betalo-sweden/await/releases/download/v0.3.0/await-linux-amd64
chmod +x await

Usage

$ await -h
Usage: await [options...] <res>... [ -- <cmd>]
Await availability of resources.

  -f	Force running the command even after giving up
  -q	Set quiet mode
  -t duration
    	Timeout duration before giving up (default 1m0s)
  -v	Set verbose output

Resources

All dependent resources must be specified as URLs or escaped command.

Some resources provided additional functionally encoded as fragment (#<fragment>). The syntax is as follows: k1|k1=v1,v2,v3...[&k2=v1&...] (no quoting supported). E.g.: http://example.com/#ssl&foo=bar,baz&i=j

Valid resources are: HTTP, Websocket, TCP, File, PostgreSQL, MySQL, Command.

HTTP Resource

URL syntax: http[s]://[<user>[:<pass>]@]<host>[:<port>][<path>][?<query>]

Websocket Resource

URL syntax: ws[s]://[<user>[:<pass>]@]<host>[:<port>][<path>][?<query>]

TCP Resource

URL syntax: tcp[4|6]://<host>[:<port>]

File Resource

URL syntax: file://<path>[#<fragment>]

• absent key: If present, the resource is defined as available, when the specific file is absent, rather than existing.

PostgreSQL Resource

URL syntax: postgres://[<user>[:<pass>]@]<host>[:<port>][/<dbname>][?<dbparams>][#<fragment>]

The URL defines a DSN.

The database name <dbname> is optional. If provided, the resource is classified as available as soon as the database was found.

DB Parameters:

• sslmode=[verify-ca|require]: sslmode=verify-ca enables TLS/SSL encrypted connection to the server. Use sslmode=require if you want to use a self-signed or invalid certificate (server side). See lib/pq for more details.

Fragment:

• tables[=t1,t2,...] key-value: If key present and value absent, the resource's database scheme must at least contain one table. If key present and value present, the resource's database scheme must at least contain the specified tables. Using this key requires to provide a database name.

MySQL Resource

URL syntax: mysql://[<user>[:<pass>]@]<host>[:<port>][/<dbname>][?<dbparams>][#<fragment>]

The URL defines a DSN.

The database name <dbname> is optional. If provided, the resource is classified as available as soon as the database was found.

DB Parameters:

• tls=[true|skip-verify]: tls=true enables TLS/SSL encrypted connection to the server. Use tls=skip-verify if you want to use a self-signed or invalid certificate (server side). See go-sql-driver/mysql for more details.

Fragment:

• tables[=t1,t2,...] key-value: If key present and value absent, the resource's database scheme must at least contain one table. If key present and value present, the resource's database scheme must at least contain the specified tables. Using this key requires to provide a database name.

Command Resource

Does not follow the URL syntax and is used a generic fallback for invalid URLs (i.e. absent scheme).

URL syntax: <path> [<arg>...]

Alternatives

Once Docker-Compose support the Docker HEALTHCHECK directive for awaiting services being up, this tool could become deprecated.

Many alternative solutions exist, most of them avoiding to interpret the resource type, leaving only options like tcp and http, or having a specific focus on Docker Compose. A few of them listed below:

• ContainerPilot
• controlled-compose
• crane
• docker-wait
• dockerize
• wait-for-it
• wait_for_db
• wait_to_start.sh
• waitforservices

License

MIT License. See LICENSE.