README ¶
goenvtemplator
Tool to template configuration files by environment variables and optionally replace itself with the target binary.
goenvtemplator is a simple app, that can template your config files by environment variables and optionally replace itself (by exec syscall) with the application binary. So at the end your application runs directly under the process that run this tool like docker as if it was originally the entrypoint itself.
This tool is ideal for use without polluting you environment with dependencies. It is fully statically linked so it has no dependencies whatsoever. If you use Dockerfile you don't even need wget or curl since it can be installed only by dockerfile's ADD instruction.
Installation
wget
wget https://github.com/seznam/goenvtemplator/releases/download/v2.0.0/goenvtemplator-amd64 -O /usr/local/bin/goenvtemplator2
chmod +x /usr/local/bin/goenvtemplator2
Dockerfile
ADD https://github.com/seznam/goenvtemplator/releases/download/v2.0.0/goenvtemplator-amd64 /usr/local/bin/goenvtemplator2
RUN chmod +x /usr/local/bin/goenvtemplator2
Building from source
# if you have glide already get the binary
go get github.com/Masterminds/glide
# install dependencies
$GOPATH/bin/glide i
make
Usage
goenvtemplator2 -help
Usage of goenvtemplator2:
-debug-templates
Print processed templates to stdout.
-delim-left string
Override default left delimiter {{.
-delim-right string
Override default right delimiter }}.
-env-file value
Additional file with environment variables. Can be passed multiple times.
-exec
Activates exec by command. First non-flag arguments is the command, the rest are it's arguments.
-template value
Template (/template:/dest). Can be passed multiple times.
-v int
Verbosity level.
-version
Prints version.
Example
goenvtemplator2 -template /path/to/server.conf.tmpl:/path/to/server.conf -template /path/to/server2.conf.tmpl:/path/to/server2.conf
Dockerfile
ENTRYPOINT ["/usr/local/bin/goenvtemplator2", "-template", "/path/to/server.conf.tmpl:/path/to/server.conf", "-exec"]
CMD ["/usr/bin/server-binary", "server-argument1", "server-argument2", "..."]
Env files
It is possible to add additional environment variables in multiple env-files. Existing variables are not overwritten. Environment variables in files can be formated using shell syntax or yaml syntax.
Let us consider an environment file myenvfile
bellow.
# cat myenvfile
A=a
B=b
B=bb
#B=bbb
export C=c
# yaml syntax
D: d
E=$A
The behaviour of env-file argument and env variables evaluation is as follows:
goenvtemplator2 -env-file myenvfile -exec sh -c 'echo $A'
> a
export A=foo
goenvtemplator2 -env-file myenvfile -exec sh -c 'echo $A'
> foo
goenvtemplator2 -env-file myenvfile -exec sh -c 'echo $B'
> bb
goenvtemplator2 -env-file myenvfile -exec sh -c 'echo $C'
> c
goenvtemplator2 -env-file myenvfile -exec sh -c 'echo $D'
> d
goenvtemplator2 -env-file myenvfile -exec sh -c 'echo $E'
> a
For more information about env-files features see github.com/joho/godotenv documentation, which goenvtemplator internally uses as a library.
Using Templates
Templates use Golang text/template and Sprig library.
Built-in functions
There are a few built in functions as well:
{{ required "Error message" Value }}
- Raises an error ifValue
is nil or it is equal to empty string. For example{{ required "TIMEOUT_MS must be set!" (env "TIMEOUT_MS) }}
{{ range $key, $value := envall }}{{ $key }}={{ $value }};{{ end }}
- Loop over every environment variable.
Nested Go templates
If you have nested Go templates there is problem with escaping. To resolve this problem you can define different
delimiters of template tags using -delim-left
and -delim-right
command line arguments.
Example of templating with [[ ]]
instead of {{ }}
delimiters
goenvtemplator2 -template /foo/bar.tmpl:/bar/foo.conf -delim-left [[ -delim-right ]]
Documentation ¶
There is no documentation for this package.