docker快速入門

by Shubheksha

通過Shubheksha

Docker標(biāo)簽快速入門 (A quick introduction to Docker tags)

If you’ve worked with Docker even for a little while, I bet you’ve come across tags. They often look like “my_image_name:1” where the part after the colon is known as a tag. The tag is not always specified when tagging images, but we’ll get to the bottom of that later.

如果您與Docker一起工作了一段時(shí)間，我敢打賭您會(huì)碰到標(biāo)簽。 它們通常看起來像“ my_image_name：1”，其中冒號(hào)后面的部分稱為標(biāo)簽。 標(biāo)記圖像時(shí)并不總是指定該標(biāo)記，但是稍后我們將介紹它。

Ever since I started using Docker, I’ve been very confused about tags. The documentation doesn’t explain them very well, and there really aren’t any thorough explanations on the topic. That’s why I decided to write this post.

自從我開始使用Docker以來，我一直對(duì)標(biāo)簽感到困惑。 該文檔對(duì)它們的解釋不是很好，并且對(duì)此主題確實(shí)沒有任何詳盡的解釋。 這就是為什么我決定寫這篇文章的原因。

什么是Docker標(biāo)簽？ (What are Docker tags?)

So, what exactly are Docker tags? In simple words, Docker tags convey useful information about a specific image version/variant. They are aliases to the ID of your image which often look like this: f1477ec11d12. It’s just a way of referring to your image. A good analogy is how Git tags refer to a particular commit in your history.

那么，Docker標(biāo)簽到底是什么？ 簡(jiǎn)而言之，Docker標(biāo)記傳達(dá)有關(guān)特定映像版本/變量的有用信息。 它們是圖像ID的別名，通常看起來像這樣： f1477ec11d12 。 這只是引用您的圖片的一種方式。 一個(gè)很好的類比是Git標(biāo)簽如何引用歷史記錄中的特定提交。

The two most common cases where tags come into play are:

標(biāo)簽起作用的兩種最常見的情況是：

When building an image, we use the following command:

構(gòu)建圖像時(shí)，我們使用以下命令：

docker build -t username/image_name:tag_name .

Let’s try to unpack what this command does for a bit. We tell the Docker daemon to fetch the Docker file present in the current directory (that’s what the . at the end does). Next, we tell the Docker daemon to build the image and give it the specified tag. If you run docker images, you should see an image whose repository is username/image_name and tag is tag_name.

讓我們嘗試解壓縮該命令的功能。 我們告訴Docker守護(hù)進(jìn)程獲取當(dāng)前目錄中存在的Docker文件(這就是.結(jié)尾的意思)。 接下來，我們告訴Docker守護(hù)程序構(gòu)建映像并為其指定指定標(biāo)簽。 如果運(yùn)行docker images ，應(yīng)該會(huì)看到一個(gè)鏡像，其存儲(chǔ)庫(kù)為username/image_name ，標(biāo)簽為tag_name 。

username/image_name is not a mandatory format for specifying the name of the image. It’s just a useful convention to avoid tagging your image again when you need to push it to a registry.

username/image_name不是用于指定圖像名稱的強(qiáng)制格式。 這只是一個(gè)有用的約定，可以避免在需要將圖像推送到注冊(cè)表時(shí)再次對(duì)其進(jìn)行標(biāo)記。

Your image can be named anything you want. For the public Docker registry, you’re restricted to a two level hierarchy while naming images. For example, your image cannot have the name a/b/c:1. This restriction usually doesn’t exist in private registries. As stated before, it’s not mandatory to specify a tag_name. We’ll see what happens in that case soon.

您的圖像可以命名為任何您想要的名稱。 對(duì)于公共Docker注冊(cè)表，在命名映像時(shí)僅限于兩級(jí)層次結(jié)構(gòu)。 例如，您的圖片名稱不能為a/b/c:1. 此限制通常在私人注冊(cè)表中不存在。 如前所述，指定tag_name.不是強(qiáng)制性的tag_name. 我們將很快看到在這種情況下會(huì)發(fā)生什么。

2. Explicitly tagging an image through the tag command.

2.通過tag命令明確標(biāo)記圖像。

docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]

This command just creates an alias (a reference) by the name of the TARGET_IMAGE that refers to the SOURCE_IMAGE. That’s all it does. It’s like assigning an existing image another name to refer to it. Notice how the tag is specified as optional here as well, by the [:TAG] .

此命令僅通過引用SOURCE_IMAGE.的TARGET_IMAGE的名稱創(chuàng)建別名(引用) SOURCE_IMAGE. 這就是全部。 這就像為現(xiàn)有圖像分配另一個(gè)名稱來引用它一樣。 注意這里的[:TAG]也將標(biāo)簽指定為可選[:TAG] 。

如果不指定標(biāo)簽會(huì)怎樣？ (What happens when you don’t specify a tag?)

Alright, now let’s uncover what happens when you don’t specify a tag while tagging an image. This is where the latest tag comes into the picture. Whenever an image is tagged without an explicit tag, it’s given the latest tag by default. It’s an unfortunate naming choice that causes a lot of confusion. But I like to think of it as the default tag that’s given to images when you don’t specify one.

好了，現(xiàn)在讓我們發(fā)現(xiàn)在標(biāo)記圖像時(shí)未指定標(biāo)記時(shí)會(huì)發(fā)生什么。 這是latest標(biāo)簽進(jìn)入圖片的地方。 每當(dāng)為圖像添加標(biāo)簽而沒有顯式標(biāo)簽時(shí)，默認(rèn)情況下都會(huì)為其賦予latest標(biāo)簽。 這是一個(gè)不幸的命名選擇，引起了很多混亂。 但我想將其視為未指定圖像時(shí)賦予圖像的默認(rèn)標(biāo)記 。

A lot of confusion around latest is caused due to the expectation that it’s the latest version of the image, especially in Dockerfiles. Let’s consider the various scenarios with an example:

人們對(duì)latest的困惑是由于人們期望它是映像的最新版本，尤其是在Dockerfiles中。 讓我們以一個(gè)示例來考慮各種場(chǎng)景：

方案1： (Scenario 1:)

Suppose the following statement is present in our Dockerfile:

假設(shè)在我們的Dockerfile中存在以下語句：

FROM debian

Since we didn’t specify any tag, Docker will add the latest tag and try to pull the image debian:latest .

由于我們未指定任何標(biāo)簽，因此Docker將添加latest標(biāo)簽并嘗試提取圖像debian:latest 。

方案2： (Scenario 2:)

FROM debian:9.3

Since the tag is explicitly mentioned here, Docker will pull the Debian image tagged 9.3

由于此處已明確提及該標(biāo)簽，因此Docker將提取標(biāo)記為9.3的Debian映像。

Another thing to keep in mind is that there is no rule which states that an image needs to have just one tag. An image can have multiple tags and they’re usually used to specify major and minor versions. For example, consider this:

要記住的另一件事是，沒有規(guī)則指出圖像只需要一個(gè)標(biāo)簽。 一個(gè)圖像可以有多個(gè)標(biāo)簽，它們通常用于指定主要和次要版本。 例如，考慮一下：

At the time of writing this post, the latest tag for the Debian image points to the 9.3 release and the 9 release. This will most likely change in the future whenever the major or minor version is bumped for the image.

在撰寫本文時(shí)，Debian映像的latest標(biāo)簽指向9.3版本和 9版本。 每當(dāng)更改主要或次要版本的映像時(shí)，將來這種情況很可能會(huì)改變。

Please note that tags being used for semantic versioning is a convention that’s followed, but tags weren’t designed just for that purpose.

請(qǐng)注意，用于語義版本控制的標(biāo)簽是遵循的約定，但標(biāo)簽并非僅用于此目的。

總之，最新不是特殊標(biāo)簽 (In conclusion, latest is not a special tag)

The main takeaway from what we’ve covered so far is that latest is just like any other tag. The onus is on the developer to tag the images properly such that latest always points to the latest stable release of the image.

到目前為止，我們主要介紹的內(nèi)容是最新的標(biāo)簽與其他任何標(biāo)簽一樣 。 開發(fā)人員有責(zé)任正確標(biāo)記圖像，以便“ latest始終指向圖像的最新穩(wěn)定版本。

Hence, we don’t explicitly specify a tag in our Dockerfiles when pulling images, since we might end up with a completely different version of the base image than what we had used before. There is no guarantees about whether it’ll be a major bump or minor bump. Even an old release can be tagged as latest.

因此，在拉取映像時(shí)，我們不會(huì)在Dockerfile中明確指定標(biāo)簽，因?yàn)槲覀冏罱K可能會(huì)獲得與之前使用的映像完全不同的版本。 不能保證它會(huì)是主要顛簸還是次要顛簸。 甚至舊版本也可以標(biāo)記為latest 。

P.S. If you found any misconceptions/errors in the post, please feel free to tweet to me @ScribbingOn.

PS：如果您在帖子中發(fā)現(xiàn)任何誤解/錯(cuò)誤，請(qǐng)隨時(shí)通過@ScribbingOn向我發(fā)送推文。

Thanks to Jér?me Petazzoni for helping me make sense of some of this.

感謝Jér?mePetazzoni幫助我理解了其中的一些內(nèi)容。

翻譯自: https://www.freecodecamp.org/news/an-introduction-to-docker-tags-9b5395636c2a/

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