Whenever an image is tagged without an explicit tag, its given the latest tag by default. A good analogy is how Git tags refer to a particular commit in your history. This restriction usually doesnt exist in private registries. Using the above command, we can specify a new tag to a source image that and create a target image. They convey essential information about the version of a specific image. Lets try to tag an image using this command. They are aliases to the ID of your image which often look like this: f1477ec11d12. This comes into the picture when we dont specify any tags to the image. Lets discuss them one by one. Get started, freeCodeCamp is a donor-supported tax-exempt 501(c)(3) nonprofit organization (United States Federal Tax Identification Number: 82-0779546). Your image has now been pushed to the new private registry. The tag is not always specified when tagging images, but well get to the bottom of that later. For example, your image cannot have the name a/b/c:1. They can only have a maximum of 128 chars. Our mission: to help people learn to code for free. We can now use the Docker tag command to tag the ubuntu:latest image with a new tag. We can use the Docker tag command to add metadata to Docker images. It can be the creators name, version of the image, use of the image, name of the application, etc. Lets consider the various scenarios with an example: Suppose the following statement is present in our Dockerfile: Since we didnt specify any tag, Docker will add the latest tag and try to pull the image debian:latest . If youve worked with Docker even for a little while, I bet youve come across tags. We can use the Docker tag command to tag an existing Docker image in our host system. This is where the latest tag comes into the picture. You can use the following steps to create a private registry. Docker assumes that the image that we are creating is the latest version of the images in the repository and hence, it automatically embeds the latest tag to it. Tweet a thanks, Learn to code for free. You can make a tax-deductible donation here. In simple words, Docker tags convey useful information about a specific image version/variant. For example, lets check out the Dockerfile and the command below. But we need to ensure that a tag name does not begin with a dash or a period. Here, the component after colon specifies the tag of the Ubuntu image that we want to pull. We can use Docker tags to provide specific labels to an image. Docker tags allow us to group our images together by creating a unique combination of name:tag. When pulling images from Dockerhub, you might have noticed that if you dont specify the tag of the image that you want to pull, it automatically starts pulling the latest one. Even when building an image using the Docker build command, if we dont specify any tag it assigns the latest tag to it. Its like assigning an existing image another name to refer to it. You can see that our new tagged image has been created. Notice how the tag is specified as optional here as well, by the [:TAG] . This command just creates an alias (a reference) by the name of the TARGET_IMAGE that refers to the SOURCE_IMAGE. at the end does). The . We can only specify tag names that contain valid ASCII characters only. Thanks to Jrme Petazzoni for helping me make sense of some of this. It automatically embeds the latest tag with the image. We dont have to provide tags to images, however, its recommended to specify a tag to keep track of the purpose of the image and its specific version. A fair analogy is how we use Git tags to refer to specific commits in history. Lets try to build this image and list all the images to verify the tag. Your image can be named anything you want. There are 3 scenarios where we use Docker tags. Ever since I started using Docker, Ive been very confused about tags. The two most common cases where tags come into play are: Lets try to unpack what this command does for a bit. In this article, we are going to understand how to use the Docker tag command to tag Docker images. Well see what happens in that case soon. (dot) here specifies the location of the Dockerfile. We also have thousands of freeCodeCamp study groups around the world. When building an image, we use the following command. So, what exactly are Docker tags? Alright, now lets uncover what happens when you dont specify a tag while tagging an image. Lets check out the following scenarios. A lot of confusion around latest is caused due to the expectation that its the latest version of the image, especially in Dockerfiles. Its an unfortunate naming choice that causes a lot of confusion. Lets try to give this image a tag called myubuntu. When we use the Docker build command to build an image from a Dockerfile, we use the -t option to give a name and tag to the image. Docker Push | How to Push Docker Images to Dockerhub? For the public Docker registry, youre restricted to a two level hierarchy while naming images. But I like to think of it as the default tag thats given to images when you dont specify one. Image tags are optional. You can commit the registry container to save the changes. As already discussed above, we can use the Docker tag command to explicitly tag Docker images. If you read this far, tweet to the author to show them you care. The main takeaway from what weve covered so far is that latest is just like any other tag. Also, please check out our free Docker Tutorials. This will most likely change in the future whenever the major or minor version is bumped for the image. Anything which you think will help you to uniquely identify the image later on. If you have the ID of an existing image, you can use it to give it a new tag. Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services, and staff. Docker registries such as Docker hub store images in repositories. Docker tags help us to give a label or metadata to the images so that we can easily identify the version or purpose of the image. To pull the image back, you can use the following command. They often look like my_image_name:1 where the part after the colon is known as a tag. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. If we dont provide any tag to the image while building it, Docker automatically specifies a tag called latest to the image. We can pretty much provide any legal name as a tag to the image. There is no guarantees about whether itll be a major bump or minor bump. The onus is on the developer to tag the images properly such that latest always points to the latest stable release of the image. If we dont specify any tag, the Docker assumes that the user wants to pull the latest image from Dockerhub. Its just a way of referring to your image. 2. An image can have multiple tags and theyre usually used to specify major and minor versions. Keep the container running, and tag an already existing image that you want to push as follows . username/image_name is not a mandatory format for specifying the name of the image. We can then upload these unique images to share them on the Docker hub. Now, push your image to the registry that you just created. They can be considered an alias to image IDs. Its just a useful convention to avoid tagging your image again when you need to push it to a registry. We accomplish this by creating thousands of videos, articles, and interactive coding lessons - all freely available to the public. The documentation doesnt explain them very well, and there really arent any thorough explanations on the topic. If you run docker images, you should see an image whose repository is username/image_name and tag is tag_name. The default tag given to an image is the latest tag. When we use the FROM instruction inside a Dockerfile to pull base images from Dockerhub, we specify the tag of the image as well. For example, consider this: At the time of writing this post, the latest tag for the Debian image points to the 9.3 release and the 9 release. Before we move ahead, its recommended that you understand the following topics before jumping into Docker tags. Here, we have used the image ID of an already existing image to give that image, a new tag. Since the tag is explicitly mentioned here, Docker will pull the Debian image tagged 9.3. As stated before, its not mandatory to specify a tag_name. In case you have any queries or suggestions, please mention them in the comment box and we will have our experts get back to you. Here, we have given our image a name called myubuntuimage and a tag called version1. Even an old release can be tagged as latest. P.S. Please note that tags being used for semantic versioning is a convention thats followed, but tags werent designed just for that purpose. Explicitly tagging an image through the tag command. The image names are usually of the form . Thats why I decided to write this post. Thats all it does. We tell the Docker daemon to fetch the Docker file present in the current directory (thats what the . For example, the Ubuntu repository in the Docker hub has several Ubuntu images, but all of them have different tags such as 18.04, focal, xenial, bionic, etc. Hence, we dont 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. However, they can contain digits, periods, underscores, dashes, and both lowercase and uppercase letters. If you found any misconceptions/errors in the post, please feel free to tweet to me @ScribbingOn. First, lets list all the existing images in our machine. Moreover, specifying image tags becomes essential when we want to push the images to any repository. Another thing to keep in mind is that there is no rule which states that an image needs to have just one tag. A repository is a set of similar images but different versions identified using tags. The syntax of the Docker tag command is . 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docker tag container as image